#2126: Fix language selection drop down

[oanding-blrng]

This PR fixes #2126

Identification of root cause:

In the current setup of property files for localization, the method

IDEasy/gui/src/main/java/com/devonfw/ide/gui/nls/NlsService.java

Lines 242 to 245 in ec264ff

	private ResourceBundle loadBundle(Locale locale) {
	return ResourceBundle.getBundle(BUNDLE_NAME, locale);
	}

returns the German ResourceBundle instead of the English one (located in the root properties file) with Locale.ENGLISH as an argument. This leads to a list with only one entry for the language selection dropdown, because for both locals (en and de) the German ResourceBundle gets returned.

This behaviour is "normal" in the sense, that ResourceBundle first tries to find a properties file for en_UK, can't find one and goes up the chain for en and after that the root file. But before the root is being used, ResourceBundle also tries the system locale (for me this would return de_DE). So ResourceBundle would search for de_DE, and after that de. Because of this "missing link" in the chain for English, this results in the observed behaviour mentioned in the issue #2126. Additional information are in #2221.

Implemented changes:

• Created messages_en.properties, so the ResourceBundle can find the correct bundle and fallbacks automatically for the keys to the root properties, because no keys are being overwritten
• Extended testGetInstanceWithLocale(..) test method in NlsServiceTest.java to cover additional machine setups

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Testing instructions

Please add concise, understandable instructions on how a reviewer can test/verify the functionality of your contribution here:

1. Run the test of the GUI module with mvn test -pl gui. The tests mentioned in the issue only german is listed in language selection dropdown #2126 should pass now
2. Run the AppLauncher via RunConfiguration
3. Depending on the locale settings of the machine, the language should either be the system setting or English for the start
4. German and English are both listed in the dropdown menu and selecting a different language should take effect in the GUI

Retest:

1. Run ide gui. The language selection dropdown should now list English and German

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[hohwille]

@oanding-blrng thanks for this PR with your new approach. Looks great to me👍
I only have some rather cosmetic remarks before we will merge.

[hohwille]

2nd and 3rd param seem to lack a trailing e.

[hohwille]

Wouldn't it make sense to use this test to also test that our NLS is working in a way it can actually translate so we also test that Deutsch (de) becomes German (de) if the locale language is English and vice versa for German we would get Englisch (en) instead of English (en)?