@XionSteel
@mahtan
well we can also look at it this way, skimming the manga, he seems to have been around people speaking maybe 3 times. and because people who know him know he cant understand anything, they don't try to teach him rather than getting to the end goal of what they wanted to say.
we then have the possibility that this language is not even close to your original language, lets say its like english to chinese, where english doesn't have pronunciation inflect meaning to the words in a way that 100% changes the meaning of the word (granted, the way the word is said may impart happy, angry ect, but it wont change but it wont change 'can I use your pencil' to 'I want to eff your cat') and there is very little hope of a person who isn't use to that style of language just picking it up
unless we are giveing a time frame for him being there, it would take a normal person several months to pick anything up without being taught, and this is with full conversations happening around them all the time.