The suffix set is not the same in every language
English needs key_one and key_other. Czech and Polish need key_one, key_few, key_many and key_other. Spanish, French and Italian need one, many and other. A file copied from the English locale and translated in place ends up with two forms in a language that needs four, and the missing ones render the key.
Linguiqo lays out the boxes a language actually has and writes exactly those keys back.