Enable setting the default posting language from Tusky (#2946)

* Extract locale utils

* Extract makeIcon

* Allow setting the (server-synchronized) default posting language from Tusky.
Closes #2902

* Add copyright headers

* Address review feedback

app/src/main/java/com/keylesspalace/tusky/util/LocaleExtensions.kt

@@ -1,5 +1,22 @@
+/* Copyright 2022 Tusky Contributors
+ *
+ * This file is a part of Tusky.
+ *
+ * This program is free software; you can redistribute it and/or modify it under the terms of the
+ * GNU General Public License as published by the Free Software Foundation; either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * Tusky is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
+ * the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+ * Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with Tusky; if not,
+ * see <http://www.gnu.org/licenses>. */
+
 package com.keylesspalace.tusky.util
 
+import android.content.Context
+import com.keylesspalace.tusky.R
 import java.util.Locale
 
 // When a language code has changed, `language` *explicitly* returns the obsolete version,
@@ -9,3 +26,11 @@ val Locale.modernLanguageCode: String
     get() {
         return this.toLanguageTag().split('-', limit = 2)[0]
     }
+
+fun Locale.getTuskyDisplayName(context: Context): String {
+    return context.getString(
+        R.string.language_display_name_format,
+        this?.displayLanguage,
+        this?.getDisplayLanguage(this)
+    )
+}