[wiki] Disable the ability to use locale to access non-standard files

[TPGPL]

Currently you can use ?locale=README to access the README.md file, which shouldn't be possible. The solution to this problem might be parsing only the 2-letter file names.

Example: https://osu.ppy.sh/help/wiki/Tournaments?locale=README

https://github.com/ppy/osu-wiki/tree/master/wiki/Tournaments

also for some reason setting locale to TEMPLATE for Tournaments breaks the site completely ^{maybe because of curly brackets ❓}

[kj415j45]

don't forget there's pt-br