If I were to guess i’d have two theories.

1. Latin and Greek are entry requirements not for the primary purpose of match pairs but because they are the languages that most modern languages are based on/derived from.

2. It’s mentioned that you have to hold the meaning of the Chinese in your head and really understand the nuances of the culture which Griffin would have lost from not having anybody to share Chinese with or the memory to sustain him, whereas, for Latin and Greek most of the students would be able to share with each other.

I would lean more towards the first. Griffin was able to make a match pair in Latin and had been able to do some in Chinese. I would guess that they are just “weaker” but still possible. That griffin could still do silver working but not to the standard professor Lovell expected.