Settings GUI: Use language names rather than codes

[rubenwardy]

Part of #13476

Showing language codes isn't very user friendly. This PR makes it so the language dropdown shows the local name for the language.

This is also a prerequisite to making other drop downs translatable (for that, I'll need to update the settingtypes parser to create these labels and update translation templates. For a future PR).

To do

This PR is Ready for Review

How to test

• Open settings GUI > user interfaces
• See dropdown

[grorp]

Slightly related: To help with #9141, we could add language as the first setting in the "Accessibility" category (as this category is the first thing you see when you open the settings).

diff --git a/builtin/mainmenu/settings/dlg_settings.lua b/builtin/mainmenu/settings/dlg_settings.lua
index b8d99a469..6049729a4 100644
--- a/builtin/mainmenu/settings/dlg_settings.lua
+++ b/builtin/mainmenu/settings/dlg_settings.lua
@@ -68,6 +68,8 @@ add_page({
        id = "accessibility",
        title = gettext("Accessibility"),
        content = {
+               "language",
+               { heading = gettext("General") },
                "font_size",
                "chat_font_size",
                "gui_scaling",

It even makes sense: One could argue that localization is an accessibility feature.

Screenshot

[srifqi]

(See comments on lines for the requests)

PS grorp's suggestion is good, too.

[grorp]

Works, code looks good.

[srifqi]

The PR looks good to me. (If any) naming errors can be addressed later.

PS I really want to invite the Minetest translators for checking these local names, but that is highly unlikely and will just cause delays.