Translation:Hello, this is my younger brother.
In what context can this be used. When someone says "hello this is George" I interpret it as George is the name of the speaker. When would someone say "hello this is my younger brother"?
Would "junior" be a good translation for младший, since it can't be confused as comparative the same way "younger" can be?
This sounds incredibly unnatural to me (Hiberno- and British-English speaker).
I would refer to my brother most often as my "little brother" (even if he is now in his 20s) or my "younger brother". Then again, I only have one brother, so the adjective is quite superfluous!