Of course, focusing on unknown words can bring good results in many cases. But, for several reasons, it can also failed:
- since you are working with limited vocabs, depending on the way you built them, a word can be in a dict of one language and not in the other.
- you can have an unknown word in the input sentence, and ONMT will construct a translation with only known words, or the contrary.
- an unknown rare word in a language can have a translation built from very current words in the other
- there is often a N-words to M-words match to find.