refactor(build): graduate HAVE_LOCALE_H feature

Merge locale.h into os/lang.h
Having a source file with the same name as a system header we use is
considered an anti-pattern.

12 files changed, 346 insertions, 410 deletions

diff --git a/cmake.config/CMakeLists.txt b/cmake.config/CMakeLists.txt
index 7e8c7ecd16..6bf4a60cf1 100644
--- a/cmake.config/CMakeLists.txt
+++ b/cmake.config/CMakeLists.txt
@@ -35,7 +35,6 @@ check_symbol_exists(_NSGetEnviron crt_externs.h HAVE__NSGETENVIRON)
 
 # Headers
 check_include_files(langinfo.h HAVE_LANGINFO_H)
-check_include_files(locale.h HAVE_LOCALE_H)
 check_include_files(strings.h HAVE_STRINGS_H)
 check_include_files(sys/utsname.h HAVE_SYS_UTSNAME_H)
 check_include_files(termios.h HAVE_TERMIOS_H)
diff --git a/cmake.config/config.h.in b/cmake.config/config.h.in
index a1b46f8cb5..87b39e8f6f 100644
--- a/cmake.config/config.h.in
+++ b/cmake.config/config.h.in
@@ -18,7 +18,6 @@
 #cmakedefine HAVE_FD_CLOEXEC
 #cmakedefine HAVE_FSEEKO
 #cmakedefine HAVE_LANGINFO_H
-#cmakedefine HAVE_LOCALE_H
 #cmakedefine HAVE_NL_LANGINFO_CODESET
 #cmakedefine HAVE_NL_MSG_CAT_CNTR
 #cmakedefine HAVE_PWD_FUNCS
diff --git a/src/nvim/cmdexpand.c b/src/nvim/cmdexpand.c
index fcd6a73b2d..18d35e1e20 100644
--- a/src/nvim/cmdexpand.c
+++ b/src/nvim/cmdexpand.c
@@ -40,7 +40,6 @@
 #include "nvim/highlight_defs.h"
 #include "nvim/highlight_group.h"
 #include "nvim/keycodes.h"
-#include "nvim/locale.h"
 #include "nvim/log.h"
 #include "nvim/lua/executor.h"
 #include "nvim/macros.h"
@@ -50,6 +49,7 @@
 #include "nvim/menu.h"
 #include "nvim/message.h"
 #include "nvim/option.h"
+#include "nvim/os/lang.h"
 #include "nvim/os/os.h"
 #include "nvim/path.h"
 #include "nvim/popupmenu.h"
diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index 0fbf31a8cd..da2a88346a 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -45,7 +45,6 @@
 #include "nvim/insexpand.h"
 #include "nvim/keycodes.h"
 #include "nvim/lib/queue.h"
-#include "nvim/locale.h"
 #include "nvim/lua/executor.h"
 #include "nvim/macros.h"
 #include "nvim/main.h"
@@ -62,6 +61,7 @@
 #include "nvim/optionstr.h"
 #include "nvim/os/fileio.h"
 #include "nvim/os/fs_defs.h"
+#include "nvim/os/lang.h"
 #include "nvim/os/os.h"
 #include "nvim/os/shell.h"
 #include "nvim/os/stdpaths_defs.h"
diff --git a/src/nvim/generators/gen_ex_cmds.lua b/src/nvim/generators/gen_ex_cmds.lua
index 0c1051b04e..935d7b333e 100644
--- a/src/nvim/generators/gen_ex_cmds.lua
+++ b/src/nvim/generators/gen_ex_cmds.lua
@@ -66,7 +66,6 @@ defsfile:write(string.format([[
 #include "nvim/ex_session.h"
 #include "nvim/help.h"
 #include "nvim/indent.h"
-#include "nvim/locale.h"
 #include "nvim/lua/executor.h"
 #include "nvim/mapping.h"
 #include "nvim/mark.h"
@@ -75,6 +74,7 @@ defsfile:write(string.format([[
 #include "nvim/message.h"
 #include "nvim/ops.h"
 #include "nvim/option.h"
+#include "nvim/os/lang.h"
 #include "nvim/profile.h"
 #include "nvim/quickfix.h"
 #include "nvim/runtime.h"
diff --git a/src/nvim/locale.c b/src/nvim/locale.c
deleted file mode 100644
index c3cfd3bedb..0000000000
--- a/src/nvim/locale.c
+++ /dev/null
@@ -1,377 +0,0 @@
-// This is an open source non-commercial project. Dear PVS-Studio, please check
-// it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
-
-// locale.c: functions for language/locale configuration
-
-#include <stdbool.h>
-#include <stdio.h>
-
-#include "auto/config.h"
-#ifdef HAVE_LOCALE_H
-# include <locale.h>
-#endif
-
-#include "nvim/ascii.h"
-#include "nvim/buffer.h"
-#include "nvim/charset.h"
-#include "nvim/eval.h"
-#include "nvim/ex_cmds_defs.h"
-#include "nvim/garray.h"
-#include "nvim/gettext.h"
-#include "nvim/locale.h"
-#include "nvim/macros.h"
-#include "nvim/memory.h"
-#include "nvim/message.h"
-#include "nvim/option.h"
-#include "nvim/os/os.h"
-#include "nvim/os/shell.h"
-#include "nvim/path.h"
-#include "nvim/profile.h"
-#include "nvim/types.h"
-#include "nvim/vim.h"
-
-#ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "locale.c.generated.h"
-#endif
-
-#if defined(HAVE_LOCALE_H)
-# define HAVE_GET_LOCALE_VAL
-
-static char *get_locale_val(int what)
-{
-  // Obtain the locale value from the libraries.
-  char *loc = setlocale(what, NULL);
-
-  return loc;
-}
-#endif
-
-/// @return  true when "lang" starts with a valid language name.
-///          Rejects NULL, empty string, "C", "C.UTF-8" and others.
-static bool is_valid_mess_lang(const char *lang)
-{
-  return lang != NULL && ASCII_ISALPHA(lang[0]) && ASCII_ISALPHA(lang[1]);
-}
-
-/// Obtain the current messages language.  Used to set the default for
-/// 'helplang'.  May return NULL or an empty string.
-char *get_mess_lang(void)
-{
-  char *p;
-
-#ifdef HAVE_GET_LOCALE_VAL
-# if defined(LC_MESSAGES)
-  p = get_locale_val(LC_MESSAGES);
-# else
-  // This is necessary for Win32, where LC_MESSAGES is not defined and $LANG
-  // may be set to the LCID number.  LC_COLLATE is the best guess, LC_TIME
-  // and LC_MONETARY may be set differently for a Japanese working in the
-  // US.
-  p = get_locale_val(LC_COLLATE);
-# endif
-#else
-  p = os_getenv("LC_ALL");
-  if (!is_valid_mess_lang(p)) {
-    p = os_getenv("LC_MESSAGES");
-    if (!is_valid_mess_lang(p)) {
-      p = os_getenv("LANG");
-    }
-  }
-#endif
-  return is_valid_mess_lang(p) ? p : NULL;
-}
-
-// Complicated #if; matches with where get_mess_env() is used below.
-#ifdef HAVE_WORKING_LIBINTL
-/// Get the language used for messages from the environment.
-static char *get_mess_env(void)
-{
-  char *p;
-
-  p = (char *)os_getenv("LC_ALL");
-  if (p == NULL) {
-    p = (char *)os_getenv("LC_MESSAGES");
-    if (p == NULL) {
-      p = (char *)os_getenv("LANG");
-      if (p != NULL && ascii_isdigit(*p)) {
-        p = NULL;                       // ignore something like "1043"
-      }
-# ifdef HAVE_GET_LOCALE_VAL
-      if (p == NULL) {
-        p = get_locale_val(LC_CTYPE);
-      }
-# endif
-    }
-  }
-  return p;
-}
-#endif
-
-/// Set the "v:lang" variable according to the current locale setting.
-/// Also do "v:lc_time"and "v:ctype".
-void set_lang_var(void)
-{
-  const char *loc;
-
-#ifdef HAVE_GET_LOCALE_VAL
-  loc = get_locale_val(LC_CTYPE);
-#else
-  // setlocale() not supported: use the default value
-  loc = "C";
-#endif
-  set_vim_var_string(VV_CTYPE, loc, -1);
-
-  // When LC_MESSAGES isn't defined use the value from $LC_MESSAGES, fall
-  // back to LC_CTYPE if it's empty.
-#ifdef HAVE_WORKING_LIBINTL
-  loc = get_mess_env();
-#elif defined(LC_MESSAGES)
-  loc = get_locale_val(LC_MESSAGES);
-#else
-  // In Windows LC_MESSAGES is not defined fallback to LC_CTYPE
-  loc = get_locale_val(LC_CTYPE);
-#endif
-  set_vim_var_string(VV_LANG, loc, -1);
-
-#ifdef HAVE_GET_LOCALE_VAL
-  loc = get_locale_val(LC_TIME);
-#endif
-  set_vim_var_string(VV_LC_TIME, loc, -1);
-
-#ifdef HAVE_GET_LOCALE_VAL
-  loc = get_locale_val(LC_COLLATE);
-#else
-  // setlocale() not supported: use the default value
-  loc = "C";
-#endif
-  set_vim_var_string(VV_COLLATE, loc, -1);
-}
-
-#if defined(HAVE_LOCALE_H)
-/// Setup to use the current locale (for ctype() and many other things).
-void init_locale(void)
-{
-  setlocale(LC_ALL, "");
-
-# ifdef LC_NUMERIC
-  // Make sure strtod() uses a decimal point, not a comma.
-  setlocale(LC_NUMERIC, "C");
-# endif
-
-  char localepath[MAXPATHL] = { 0 };
-  snprintf(localepath, sizeof(localepath), "%s", get_vim_var_str(VV_PROGPATH));
-  char *tail = path_tail_with_sep(localepath);
-  *tail = NUL;
-  tail = path_tail(localepath);
-  xstrlcpy(tail, "share/locale",
-           sizeof(localepath) - (size_t)(tail - localepath));
-  bindtextdomain(PROJECT_NAME, localepath);
-  textdomain(PROJECT_NAME);
-  TIME_MSG("locale set");
-}
-#endif
-
-#ifdef HAVE_WORKING_LIBINTL
-
-/// ":language":  Set the language (locale).
-///
-/// @param eap
-void ex_language(exarg_T *eap)
-{
-  char *loc;
-  char *p;
-  char *name;
-  int what = LC_ALL;
-  char *whatstr = "";
-# ifdef LC_MESSAGES
-#  define VIM_LC_MESSAGES LC_MESSAGES
-# else
-#  define VIM_LC_MESSAGES 6789
-# endif
-
-  name = eap->arg;
-
-  // Check for "messages {name}", "ctype {name}" or "time {name}" argument.
-  // Allow abbreviation, but require at least 3 characters to avoid
-  // confusion with a two letter language name "me" or "ct".
-  p = skiptowhite(eap->arg);
-  if ((*p == NUL || ascii_iswhite(*p)) && p - eap->arg >= 3) {
-    if (STRNICMP(eap->arg, "messages", p - eap->arg) == 0) {
-      what = VIM_LC_MESSAGES;
-      name = skipwhite(p);
-      whatstr = "messages ";
-    } else if (STRNICMP(eap->arg, "ctype", p - eap->arg) == 0) {
-      what = LC_CTYPE;
-      name = skipwhite(p);
-      whatstr = "ctype ";
-    } else if (STRNICMP(eap->arg, "time", p - eap->arg) == 0) {
-      what = LC_TIME;
-      name = skipwhite(p);
-      whatstr = "time ";
-    } else if (STRNICMP(eap->arg, "collate", p - eap->arg) == 0) {
-      what = LC_COLLATE;
-      name = skipwhite(p);
-      whatstr = "collate ";
-    }
-  }
-
-  if (*name == NUL) {
-    if (what == VIM_LC_MESSAGES) {
-      p = get_mess_env();
-    } else {
-      p = setlocale(what, NULL);
-    }
-    if (p == NULL || *p == NUL) {
-      p = "Unknown";
-    }
-    smsg(_("Current %slanguage: \"%s\""), whatstr, p);
-  } else {
-# ifndef LC_MESSAGES
-    if (what == VIM_LC_MESSAGES) {
-      loc = "";
-    } else {
-# endif
-    loc = setlocale(what, name);
-# ifdef LC_NUMERIC
-    // Make sure strtod() uses a decimal point, not a comma.
-    setlocale(LC_NUMERIC, "C");
-# endif
-# ifndef LC_MESSAGES
-  }
-# endif
-    if (loc == NULL) {
-      semsg(_("E197: Cannot set language to \"%s\""), name);
-    } else {
-# ifdef HAVE_NL_MSG_CAT_CNTR
-      // Need to do this for GNU gettext, otherwise cached translations
-      // will be used again.
-      extern int _nl_msg_cat_cntr;
-
-      _nl_msg_cat_cntr++;
-# endif
-      // Reset $LC_ALL, otherwise it would overrule everything.
-      os_setenv("LC_ALL", "", 1);
-
-      if (what != LC_TIME && what != LC_COLLATE) {
-        // Tell gettext() what to translate to.  It apparently doesn't
-        // use the currently effective locale.
-        if (what == LC_ALL) {
-          os_setenv("LANG", name, 1);
-
-          // Clear $LANGUAGE because GNU gettext uses it.
-          os_setenv("LANGUAGE", "", 1);
-        }
-        if (what != LC_CTYPE) {
-          os_setenv("LC_MESSAGES", name, 1);
-          set_helplang_default(name);
-        }
-      }
-
-      // Set v:lang, v:lc_time, v:collate and v:ctype to the final result.
-      set_lang_var();
-      maketitle();
-    }
-  }
-}
-
-static char **locales = NULL;       // Array of all available locales
-
-# ifndef MSWIN
-static bool did_init_locales = false;
-
-/// @return  an array of strings for all available locales + NULL for the
-///          last element or,
-///          NULL in case of error.
-static char **find_locales(void)
-{
-  garray_T locales_ga;
-  char *loc;
-  char *saveptr = NULL;
-
-  // Find all available locales by running command "locale -a".  If this
-  // doesn't work we won't have completion.
-  char *locale_a = get_cmd_output("locale -a", NULL, kShellOptSilent, NULL);
-  if (locale_a == NULL) {
-    return NULL;
-  }
-  ga_init(&locales_ga, sizeof(char *), 20);
-
-  // Transform locale_a string where each locale is separated by "\n"
-  // into an array of locale strings.
-  loc = os_strtok(locale_a, "\n", &saveptr);
-
-  while (loc != NULL) {
-    loc = xstrdup(loc);
-    GA_APPEND(char *, &locales_ga, loc);
-    loc = os_strtok(NULL, "\n", &saveptr);
-  }
-  xfree(locale_a);
-  // Guarantee that .ga_data is NULL terminated
-  ga_grow(&locales_ga, 1);
-  ((char **)locales_ga.ga_data)[locales_ga.ga_len] = NULL;
-  return locales_ga.ga_data;
-}
-# endif
-
-/// Lazy initialization of all available locales.
-static void init_locales(void)
-{
-# ifndef MSWIN
-  if (did_init_locales) {
-    return;
-  }
-
-  did_init_locales = true;
-  locales = find_locales();
-# endif
-}
-
-# if defined(EXITFREE)
-void free_locales(void)
-{
-  if (locales == NULL) {
-    return;
-  }
-
-  for (int i = 0; locales[i] != NULL; i++) {
-    xfree(locales[i]);
-  }
-  XFREE_CLEAR(locales);
-}
-# endif
-
-/// Function given to ExpandGeneric() to obtain the possible arguments of the
-/// ":language" command.
-char *get_lang_arg(expand_T *xp, int idx)
-{
-  if (idx == 0) {
-    return "messages";
-  }
-  if (idx == 1) {
-    return "ctype";
-  }
-  if (idx == 2) {
-    return "time";
-  }
-  if (idx == 3) {
-    return "collate";
-  }
-
-  init_locales();
-  if (locales == NULL) {
-    return NULL;
-  }
-  return locales[idx - 4];
-}
-
-/// Function given to ExpandGeneric() to obtain the available locales.
-char *get_locales(expand_T *xp, int idx)
-{
-  init_locales();
-  if (locales == NULL) {
-    return NULL;
-  }
-  return locales[idx];
-}
-
-#endif
diff --git a/src/nvim/locale.h b/src/nvim/locale.h
deleted file mode 100644
index 39735d371f..0000000000
--- a/src/nvim/locale.h
+++ /dev/null
@@ -1,10 +0,0 @@
-#ifndef NVIM_LOCALE_H
-#define NVIM_LOCALE_H
-
-#include "nvim/ex_cmds_defs.h"
-#include "nvim/types.h"
-
-#ifdef INCLUDE_GENERATED_DECLARATIONS
-# include "locale.h.generated.h"
-#endif
-#endif  // NVIM_LOCALE_H
diff --git a/src/nvim/main.c b/src/nvim/main.c
index 975772169b..71c5c2af46 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -41,7 +41,6 @@
 #include "nvim/highlight.h"
 #include "nvim/highlight_group.h"
 #include "nvim/keycodes.h"
-#include "nvim/locale.h"
 #include "nvim/log.h"
 #include "nvim/lua/executor.h"
 #include "nvim/macros.h"
@@ -60,6 +59,7 @@
 #include "nvim/optionstr.h"
 #include "nvim/os/fileio.h"
 #include "nvim/os/input.h"
+#include "nvim/os/lang.h"
 #include "nvim/os/os.h"
 #include "nvim/os/stdpaths_defs.h"
 #include "nvim/os/time.h"
@@ -192,12 +192,10 @@ void early_init(mparm_T *paramp)
 
   TIME_MSG("early init");
 
-#if defined(HAVE_LOCALE_H)
   // Setup to use the current locale (for ctype() and many other things).
   // NOTE: Translated messages with encodings other than latin1 will not
   // work until set_init_1() has been called!
   init_locale();
-#endif
 
   // tabpage local options (p_ch) must be set before allocating first tabpage.
   set_init_tablocal();
diff --git a/src/nvim/mbyte.c b/src/nvim/mbyte.c
index e27bb003e7..d8be4f4997 100644
--- a/src/nvim/mbyte.c
+++ b/src/nvim/mbyte.c
@@ -29,6 +29,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <iconv.h>
+#include <locale.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -67,10 +68,6 @@
 #include "nvim/types.h"
 #include "nvim/vim.h"
 
-#ifdef HAVE_LOCALE_H
-# include <locale.h>
-#endif
-
 typedef struct {
   int rangeStart;
   int rangeEnd;
@@ -2193,10 +2190,7 @@ char *enc_locale(void)
   if (!(s = nl_langinfo(CODESET)) || *s == NUL)
 #endif
   {
-#if defined(HAVE_LOCALE_H)
-    if (!(s = setlocale(LC_CTYPE, NULL)) || *s == NUL)
-#endif
-    {
+    if (!(s = setlocale(LC_CTYPE, NULL)) || *s == NUL) {
       if ((s = os_getenv("LC_ALL"))) {
         if ((s = os_getenv("LC_CTYPE"))) {
           s = os_getenv("LANG");
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 0303f0bccd..6ddc3b5cfb 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -62,7 +62,6 @@
 #include "nvim/indent_c.h"
 #include "nvim/insexpand.h"
 #include "nvim/keycodes.h"
-#include "nvim/locale.h"
 #include "nvim/log.h"
 #include "nvim/lua/executor.h"
 #include "nvim/macros.h"
diff --git a/src/nvim/os/lang.c b/src/nvim/os/lang.c
index 57c82bba86..8ca2aa3a4b 100644
--- a/src/nvim/os/lang.c
+++ b/src/nvim/os/lang.c
@@ -7,16 +7,347 @@
 # include <CoreServices/CoreServices.h>
 # undef Boolean
 # undef FileInfo
+#endif
 
-# include "auto/config.h"
-# ifdef HAVE_LOCALE_H
-#  include <locale.h>
-# endif
-# include "nvim/os/os.h"
+#include <locale.h>
+#include <stdbool.h>
+#include <stdio.h>
+
+#include "auto/config.h"
+#include "nvim/ascii.h"
+#include "nvim/buffer.h"
+#include "nvim/charset.h"
+#include "nvim/eval.h"
+#include "nvim/ex_cmds_defs.h"
+#include "nvim/garray.h"
+#include "nvim/gettext.h"
+#include "nvim/macros.h"
+#include "nvim/memory.h"
+#include "nvim/message.h"
+#include "nvim/option.h"
+#include "nvim/os/lang.h"
+#include "nvim/os/os.h"
+#include "nvim/os/shell.h"
+#include "nvim/path.h"
+#include "nvim/profile.h"
+#include "nvim/types.h"
+#include "nvim/vim.h"
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "os/lang.c.generated.h"
 #endif
 
-#include "nvim/os/lang.h"
+static char *get_locale_val(int what)
+{
+  // Obtain the locale value from the libraries.
+  char *loc = setlocale(what, NULL);
+
+  return loc;
+}
+
+/// @return  true when "lang" starts with a valid language name.
+///          Rejects NULL, empty string, "C", "C.UTF-8" and others.
+static bool is_valid_mess_lang(const char *lang)
+{
+  return lang != NULL && ASCII_ISALPHA(lang[0]) && ASCII_ISALPHA(lang[1]);
+}
+
+/// Obtain the current messages language.  Used to set the default for
+/// 'helplang'.  May return NULL or an empty string.
+char *get_mess_lang(void)
+{
+  char *p;
+
+#if defined(LC_MESSAGES)
+  p = get_locale_val(LC_MESSAGES);
+#else
+  // This is necessary for Win32, where LC_MESSAGES is not defined and $LANG
+  // may be set to the LCID number.  LC_COLLATE is the best guess, LC_TIME
+  // and LC_MONETARY may be set differently for a Japanese working in the
+  // US.
+  p = get_locale_val(LC_COLLATE);
+#endif
+  return is_valid_mess_lang(p) ? p : NULL;
+}
+
+// Complicated #if; matches with where get_mess_env() is used below.
+#ifdef HAVE_WORKING_LIBINTL
+/// Get the language used for messages from the environment.
+static char *get_mess_env(void)
+{
+  char *p;
+
+  p = (char *)os_getenv("LC_ALL");
+  if (p == NULL) {
+    p = (char *)os_getenv("LC_MESSAGES");
+    if (p == NULL) {
+      p = (char *)os_getenv("LANG");
+      if (p != NULL && ascii_isdigit(*p)) {
+        p = NULL;                       // ignore something like "1043"
+      }
+      if (p == NULL) {
+        p = get_locale_val(LC_CTYPE);
+      }
+    }
+  }
+  return p;
+}
+#endif
+
+/// Set the "v:lang" variable according to the current locale setting.
+/// Also do "v:lc_time"and "v:ctype".
+void set_lang_var(void)
+{
+  const char *loc;
+
+  loc = get_locale_val(LC_CTYPE);
+  set_vim_var_string(VV_CTYPE, loc, -1);
+
+  // When LC_MESSAGES isn't defined use the value from $LC_MESSAGES, fall
+  // back to LC_CTYPE if it's empty.
+#ifdef HAVE_WORKING_LIBINTL
+  loc = get_mess_env();
+#elif defined(LC_MESSAGES)
+  loc = get_locale_val(LC_MESSAGES);
+#else
+  // In Windows LC_MESSAGES is not defined fallback to LC_CTYPE
+  loc = get_locale_val(LC_CTYPE);
+#endif
+  set_vim_var_string(VV_LANG, loc, -1);
+
+  loc = get_locale_val(LC_TIME);
+  set_vim_var_string(VV_LC_TIME, loc, -1);
+
+  loc = get_locale_val(LC_COLLATE);
+  set_vim_var_string(VV_COLLATE, loc, -1);
+}
+
+/// Setup to use the current locale (for ctype() and many other things).
+void init_locale(void)
+{
+  setlocale(LC_ALL, "");
+
+#ifdef LC_NUMERIC
+  // Make sure strtod() uses a decimal point, not a comma.
+  setlocale(LC_NUMERIC, "C");
+#endif
+
+  char localepath[MAXPATHL] = { 0 };
+  snprintf(localepath, sizeof(localepath), "%s", get_vim_var_str(VV_PROGPATH));
+  char *tail = path_tail_with_sep(localepath);
+  *tail = NUL;
+  tail = path_tail(localepath);
+  xstrlcpy(tail, "share/locale",
+           sizeof(localepath) - (size_t)(tail - localepath));
+  bindtextdomain(PROJECT_NAME, localepath);
+  textdomain(PROJECT_NAME);
+  TIME_MSG("locale set");
+}
+
+#ifdef HAVE_WORKING_LIBINTL
+
+/// ":language":  Set the language (locale).
+///
+/// @param eap
+void ex_language(exarg_T *eap)
+{
+  char *loc;
+  char *p;
+  char *name;
+  int what = LC_ALL;
+  char *whatstr = "";
+# ifdef LC_MESSAGES
+#  define VIM_LC_MESSAGES LC_MESSAGES
+# else
+#  define VIM_LC_MESSAGES 6789
+# endif
+
+  name = eap->arg;
+
+  // Check for "messages {name}", "ctype {name}" or "time {name}" argument.
+  // Allow abbreviation, but require at least 3 characters to avoid
+  // confusion with a two letter language name "me" or "ct".
+  p = skiptowhite(eap->arg);
+  if ((*p == NUL || ascii_iswhite(*p)) && p - eap->arg >= 3) {
+    if (STRNICMP(eap->arg, "messages", p - eap->arg) == 0) {
+      what = VIM_LC_MESSAGES;
+      name = skipwhite(p);
+      whatstr = "messages ";
+    } else if (STRNICMP(eap->arg, "ctype", p - eap->arg) == 0) {
+      what = LC_CTYPE;
+      name = skipwhite(p);
+      whatstr = "ctype ";
+    } else if (STRNICMP(eap->arg, "time", p - eap->arg) == 0) {
+      what = LC_TIME;
+      name = skipwhite(p);
+      whatstr = "time ";
+    } else if (STRNICMP(eap->arg, "collate", p - eap->arg) == 0) {
+      what = LC_COLLATE;
+      name = skipwhite(p);
+      whatstr = "collate ";
+    }
+  }
+
+  if (*name == NUL) {
+    if (what == VIM_LC_MESSAGES) {
+      p = get_mess_env();
+    } else {
+      p = setlocale(what, NULL);
+    }
+    if (p == NULL || *p == NUL) {
+      p = "Unknown";
+    }
+    smsg(_("Current %slanguage: \"%s\""), whatstr, p);
+  } else {
+# ifndef LC_MESSAGES
+    if (what == VIM_LC_MESSAGES) {
+      loc = "";
+    } else {
+# endif
+    loc = setlocale(what, name);
+# ifdef LC_NUMERIC
+    // Make sure strtod() uses a decimal point, not a comma.
+    setlocale(LC_NUMERIC, "C");
+# endif
+# ifndef LC_MESSAGES
+  }
+# endif
+    if (loc == NULL) {
+      semsg(_("E197: Cannot set language to \"%s\""), name);
+    } else {
+# ifdef HAVE_NL_MSG_CAT_CNTR
+      // Need to do this for GNU gettext, otherwise cached translations
+      // will be used again.
+      extern int _nl_msg_cat_cntr;
+
+      _nl_msg_cat_cntr++;
+# endif
+      // Reset $LC_ALL, otherwise it would overrule everything.
+      os_setenv("LC_ALL", "", 1);
+
+      if (what != LC_TIME && what != LC_COLLATE) {
+        // Tell gettext() what to translate to.  It apparently doesn't
+        // use the currently effective locale.
+        if (what == LC_ALL) {
+          os_setenv("LANG", name, 1);
+
+          // Clear $LANGUAGE because GNU gettext uses it.
+          os_setenv("LANGUAGE", "", 1);
+        }
+        if (what != LC_CTYPE) {
+          os_setenv("LC_MESSAGES", name, 1);
+          set_helplang_default(name);
+        }
+      }
+
+      // Set v:lang, v:lc_time, v:collate and v:ctype to the final result.
+      set_lang_var();
+      maketitle();
+    }
+  }
+}
+
+static char **locales = NULL;       // Array of all available locales
+
+# ifndef MSWIN
+static bool did_init_locales = false;
+
+/// @return  an array of strings for all available locales + NULL for the
+///          last element or,
+///          NULL in case of error.
+static char **find_locales(void)
+{
+  garray_T locales_ga;
+  char *loc;
+  char *saveptr = NULL;
+
+  // Find all available locales by running command "locale -a".  If this
+  // doesn't work we won't have completion.
+  char *locale_a = get_cmd_output("locale -a", NULL, kShellOptSilent, NULL);
+  if (locale_a == NULL) {
+    return NULL;
+  }
+  ga_init(&locales_ga, sizeof(char *), 20);
+
+  // Transform locale_a string where each locale is separated by "\n"
+  // into an array of locale strings.
+  loc = os_strtok(locale_a, "\n", &saveptr);
+
+  while (loc != NULL) {
+    loc = xstrdup(loc);
+    GA_APPEND(char *, &locales_ga, loc);
+    loc = os_strtok(NULL, "\n", &saveptr);
+  }
+  xfree(locale_a);
+  // Guarantee that .ga_data is NULL terminated
+  ga_grow(&locales_ga, 1);
+  ((char **)locales_ga.ga_data)[locales_ga.ga_len] = NULL;
+  return locales_ga.ga_data;
+}
+# endif
+
+/// Lazy initialization of all available locales.
+static void init_locales(void)
+{
+# ifndef MSWIN
+  if (did_init_locales) {
+    return;
+  }
+
+  did_init_locales = true;
+  locales = find_locales();
+# endif
+}
+
+# if defined(EXITFREE)
+void free_locales(void)
+{
+  if (locales == NULL) {
+    return;
+  }
+
+  for (int i = 0; locales[i] != NULL; i++) {
+    xfree(locales[i]);
+  }
+  XFREE_CLEAR(locales);
+}
+# endif
+
+/// Function given to ExpandGeneric() to obtain the possible arguments of the
+/// ":language" command.
+char *get_lang_arg(expand_T *xp, int idx)
+{
+  if (idx == 0) {
+    return "messages";
+  }
+  if (idx == 1) {
+    return "ctype";
+  }
+  if (idx == 2) {
+    return "time";
+  }
+  if (idx == 3) {
+    return "collate";
+  }
+
+  init_locales();
+  if (locales == NULL) {
+    return NULL;
+  }
+  return locales[idx - 4];
+}
+
+/// Function given to ExpandGeneric() to obtain the available locales.
+char *get_locales(expand_T *xp, int idx)
+{
+  init_locales();
+  if (locales == NULL) {
+    return NULL;
+  }
+  return locales[idx];
+}
+
+#endif
 
 void lang_init(void)
 {
diff --git a/src/nvim/os/lang.h b/src/nvim/os/lang.h
index f60e064f57..bb1ebfb721 100644
--- a/src/nvim/os/lang.h
+++ b/src/nvim/os/lang.h
@@ -1,6 +1,9 @@
 #ifndef NVIM_OS_LANG_H
 #define NVIM_OS_LANG_H
 
+#include "nvim/ex_cmds_defs.h"
+#include "nvim/types.h"
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/lang.h.generated.h"
 #endif