diff --git a/core/settings.lua b/core/settings.lua
index c5e8a45e0..ee0e6a512 100644
--- a/core/settings.lua
+++ b/core/settings.lua
@@ -28,6 +28,8 @@ function settings:_init ()
             ]]):format(language, language, language, language))
          end
          fluent:set_locale(language)
+         os.setlocale(language)
+         SU.setenv("LANG", language)
       end,
       help = "Locale for localized language support",
    })
diff --git a/core/utilities/init.lua b/core/utilities/init.lua
index 2a9adf714..6619466bd 100644
--- a/core/utilities/init.lua
+++ b/core/utilities/init.lua
@@ -507,6 +507,34 @@ function utilities.rationWidth (target, width, ratio)
    return target
 end
 
+--- System
+-- @section system
+
+local function which_setenv ()
+   if type(_G._rusty_funcs) == "table" then
+      return _G._rusty_funcs.setenv
+   elseif pcall(require, "posix") then
+      return require("posix").stdlib.setenv
+   elseif pcall(require, "winapi") then
+      return require("winapi").setenv
+   else
+      return function (key, _)
+         utilities.warn(([[Failed to set environment variable '%s' using legacy Lua based CLI
+
+  Please use the Rust based CLI. Meanwhile expect anything depending on
+  this variable not to work. Alternatively installing the luaposix or
+  winapi LuaRocks modules will enable this from the Lua side.
+
+         ]]):format(key))
+      end
+   end
+end
+
+--- Set environment variable to take effect when executing subprocesses
+-- @tparam string key Name of environment variable, typically in all caps.
+-- @tparam string value Value to set.
+utilities.setenv = which_setenv()
+
 --- Text handling
 -- @section text
 
diff --git a/sile.rockspec.in b/sile.rockspec.in
index c69e74ef4..d6a3e6d0d 100644
--- a/sile.rockspec.in
+++ b/sile.rockspec.in
@@ -46,6 +46,12 @@ dependencies = {
    "vstruct == 2.1.1-1",
 }
 
+-- Optional deps to enable the legacy Lua CLI to have features from the Rust one
+--[[
+table.insert(dependencies, "luaposix == 36.2.1-1") -- for Unix
+table.insert(dependencies, "winapi == 1.4.2-1") -- for Windows
+]]
+
 build = {
    type = "builtin",
    modules = {},
diff --git a/spec/languages_spec.lua b/spec/languages_spec.lua
index 2264e9470..3d5b422f4 100644
--- a/spec/languages_spec.lua
+++ b/spec/languages_spec.lua
@@ -1,6 +1,13 @@
 SILE = require("core.sile")
 
 describe("Language module", function ()
+
+   it("should set env locale", function ()
+      SILE.call("language", { main = "tr" })
+      local syslang = os.getenv("LANG")
+      assert.is.equal("tr", syslang)
+   end)
+
    describe("Norwegian", function ()
       local hyphenate = SILE.showHyphenationPoints
 
diff --git a/spec/utilities_spec.lua b/spec/utilities_spec.lua
index fbb0191d7..e3a84813d 100644
--- a/spec/utilities_spec.lua
+++ b/spec/utilities_spec.lua
@@ -18,7 +18,7 @@ describe("SILE.utilities", function ()
       end)
    end)
 
-   describe("utf8_to_utf16be_hexencoded ", function ()
+   describe("utf8_to_utf16be_hexencoded", function ()
       it("should hex encode input", function ()
          local str = "foo"
          local out = "feff0066006f006f"
@@ -26,6 +26,16 @@ describe("SILE.utilities", function ()
       end)
    end)
 
+   describe("setenv", function ()
+      it("should effectively set variables before executing system commands", function ()
+         local before = os.getenv("FOO")
+         assert.is.equal(type(before), "nil")
+         SU.setenv("FOO", "bar")
+         local after = os.getenv("FOO")
+         assert.is.equal(after, "bar")
+      end)
+   end)
+
    describe("formatNumber", function ()
       local icu = require("justenoughicu")
       local icu73plus = tostring(icu.version()) >= "73.0"
diff --git a/src/lib.rs b/src/lib.rs
index ae6a911ed..996f54e79 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -19,6 +19,7 @@ pub fn start_luavm() -> crate::Result<Lua> {
     #[cfg(feature = "static")]
     crate::embed::inject_embedded_loader(&lua);
     inject_paths(&lua);
+    inject_rusty_funcs(&lua);
     load_sile(&lua);
     inject_version(&lua);
     Ok(lua)
@@ -50,6 +51,18 @@ pub fn inject_paths(lua: &Lua) {
     }
 }
 
+pub fn inject_rusty_funcs(lua: &Lua) {
+    let rusty_funcs: LuaTable = lua.create_table().unwrap();
+    let setenv: LuaFunction = lua
+        .create_function(|_, (key, value): (String, String)| {
+            env::set_var(key, value);
+            Ok(())
+        })
+        .unwrap();
+    rusty_funcs.set("setenv", setenv).unwrap();
+    lua.globals().set("_rusty_funcs", rusty_funcs).unwrap();
+}
+
 pub fn inject_version(lua: &Lua) {
     let sile: LuaTable = lua.globals().get("SILE").unwrap();
     let mut full_version: String = sile.get("full_version").unwrap();