FEATURE: Setting preferred locale and fallback manually

[Sharrnah]

Description:

Sometimes you might want the user to load a different language file, other than the systems current locale.

This adds a SetPreferredLocale() that you can call before or after for example AddTranslationsFS() and will set a custom locale. This way, the preferred language is looked up for translations.

Also added a SetLanguageOrder() function that reorders the added languages, in which case the first language is used as fallback when no locale is found.

with this, on a foreign language OS system, you can call

lang.AddTranslationsFS(Resources.Translations, "translations")
lang.SetLanguageOrder([]string{"fr"}) // sets fr as fallback language
lang.SetPreferredLocale("en-US") // use english instead of system locale

Checklist:

• [ ] Tests included.
• [ ] Lint and formatter run with no errors.
• [ ] Tests all pass.

Where applicable:

• [ ] Public APIs match existing style and have Since: line.
• [ ] Any breaking changes have a deprecation path or have been discussed.
• [ ] Check for binary size increases when importing new modules.