汉学家 = sinologist
a person who studies or is an expert in sinology (= Chinese language, literature, history, society, etc.)
Notice it wrote: 'studies or is an expert in sinology'
So even someone who isn't an expert, as long as he is seriously studying Chinese language, literature, history, society. He can still qualified as a sinologist (汉学家)
Edit: When I said 'seriously' I meant doing it full time.