To help distinguish files relevant to different languages, Android Studio uses flag icons on the file tabs. Since by convention all String resource files are called strings.xml, this makes it a lot easier to distinguish these in the editor tabs, in the project view, etc. If you don't want to see flags for languages, you can turn them off in the options panel; in the Appearance category, uncheck the "Select Flags for Languages" checkbox as shown here:
However, languages often cross multiple regions and countries, so it's not always clear which flag should be used to represent a language.
Android Studio uses multiple heuristics to guess. For example, if the language in question is also the language used by the user, the IDE will look up the corresponding country code used in that locale and pick the corresponding flag.
However, you can force Android Studio to show any flag for any language by setting the
First you'll need to know the 2 letter language code for the language; this is part of the ISO 639-1 standard. For example, for English the code is
Then you'll need to know the 2 letter region code for the country whose flag you want to use; this is part of the ISO 3166 standard. For example, for the USA the code is
Then, to describe a combination of language and region, you concatenate them together with an underscore or a dash, such as en-US or en_US. You can list combinations for multiple regions in a comma separated list.
Here, en_GB tells Android Studio to use the flag from Great Britain for the English language, and the flag from Brazil for the Portuguese language.