Fix follow-system app language to use primary locale

[wizdom13]

What is it?

• Bugfix (user facing)
• Feature (user facing) ⚠️ Your PR must target the refactor branch
• Codebase improvement (dev facing)
• Meta improvement to the project (dev facing)

Description of the changes in your PR

Fixes inconsistent/mixed UI language behavior when Android has multiple system languages configured and NewPipe is set to use the default/system app language.

The issue was reported in #13107. For example, when Android system languages are configured as:

1. English (US)
2. Japanese

some NewPipe UI strings could appear in Japanese even though the primary system language is English.

This PR fixes the locale handling so that NewPipe uses the intended primary/default app locale consistently instead of mixing strings from a secondary system language.

Changed area:

• app/src/main/java/org/schabi/newpipe/settings/ContentSettingsFragment.java

What is actually fixed?

Before this change, NewPipe could show UI strings from multiple languages when the app language was set to default/follow system and Android had more than one system language configured.

After this change, NewPipe consistently uses the expected app/system UI language. If English (US) is the primary Android language and Japanese is secondary, NewPipe UI remains in English instead of randomly mixing English and Japanese strings.

Fixes the following issue(s)

Fixes #13107

APK testing

Tested manually with the following language configurations:

• English (US) primary, Japanese secondary
• English (US) primary, English (UK) secondary, Japanese third
• Japanese primary, English (US) secondary

Checked:

• NewPipe starts without mixed UI strings.
• App language set to default/follow system works correctly.
• Explicit app language selection still works.
• Restarting the app keeps the expected language behavior.

Before/After Screenshots/Screen Record

Before:

• UI could show mixed English/Japanese strings when Android had multiple system languages.

After:

• UI consistently follows the selected/default app language.

Due diligence

• I read the contribution guidelines.
• The proposed changes follow the AI policy.
• I tested the changes using an emulator or a physical device.

[TobiGr]

Please fill in the template and exlain what is actually fixed.

[wizdom13]

Please fill in the template and exlain what is actually fixed.

Thanks, I updated the PR description and filled in the template. I also added a clearer explanation of what was fixed and linked it to #13107.

[Isira-Seneviratne]

Suggested change

	final String tag;
	if (systemLang.equals(language)) {
	final Locale systemLocale = LocaleListCompat.getAdjustedDefault().get(0);
	tag = (systemLocale == null ? Locale.getDefault() : systemLocale).toLanguageTag();
	} else {
	tag = language;
	}
	AppCompatDelegate.setApplicationLocales(LocaleListCompat.forLanguageTags(tag));
	if (systemLang.equals(language)) {
	AppCompatDelegate.setApplicationLocales(LocaleListCompat.getAdjustedDefault());
	} else {
	AppCompatDelegate.setApplicationLocales(LocaleListCompat.forLanguageTags(language));
	}