Github language tag for Repository

As far as I know, they aren't really tagged - the languages attached to them are the languages which you use in your project. Github looks through the source and figures out to the best of its ability what languages are in use.

If you go to your respository, then to the Graphs tab, you can see the language breakdown.

A repository can only be "tagged" with a single language in the search results. That language is the first from language statistics. Language statistics are computed by the open source project Linguist according to the total size of files for each language detected.

You can override language statistics using Linguist overrides. In particular, you can choose to ignore some files from statistics:

directory/to/ignore/* linguist-vendored
*.somextensiontoignore linguist-vendored

or override the detected language:

*.js linguist-language=Java