To reproduce:

1.Download and open "Test_language_5.5.2.zip" project.
2.Attach TEST.cs script to "Main Camera" Game Object.
3.Enter play mode and notice the console output.

Expected result: default system language is returned.
Actual result: English language is always returned even if it is not default system language.

Reproduced with: 5.5.0p1, 5.5.0p4, 5.5.2p4, 5.6.0f2, 2017.1.0a6
Not reproduced with: 5.3.8f1, 5.4.5p1, 5.5.0f3

Regression introduced in: 5.5.0p1