"Jap" is not an acceptable abbreviation for "Japan" or "Japanese". It is a racial slur that can be extremely hurtful to many. Please don't use it.
Spell out "Japanese" or use an alternate abbreviation: "jpn" and "jpns" are both common and acceptable.
About the slur:
Jap - Wiktionary Jap - Wikipedia, the free encyclopedia Anti-Japanese Propaganda Racist Propaganda