Every time I tell someone, whether a friend or a stranger, that I am planning to spend the morning hours of every weekday during my sabbatical in Jerusalem, studying at an English-speaking ultra-Orthodox yeshiva, almost everyone asks me, and that with good reason, why I will not study at a Hebrew-speaking modern Orthodox yeshiva, which seems to them to be a more natural option for me. Here is my public reply.
First of all, I believe that one of the benefits or even obligations of a sabbatical is to break the routine. This can be done ideally by living in a foreign country. But since this is not a practical option for me, the best I can do is to spend at least part of my sabbatical in as different an environment as possible within Jerusalem.
Secondly, I feel (and have seen) that ultra-Orthodox yeshivas are more "authentic" than their modern Orthodox (or "national religious") counterparts in a number of respects. Being a linguist who prefers tradition to innovation, I like the fact that the former still preserve the traditional Ashkenazic pronunciation in reading the Tora and the Talmud and davening, even when their mother tongue is Modern Hebrew, while the latter have completely abandoned this traditional pronunciation. And I am also affected by the difference I have witnesses in the results of the ultra-Orthodox and modern Orthodox education, especially in derekh-erets.
Ideally, I would study at a Yiddish-speaking yeshiva, which is the closest to the yeshiva tradition. But this option is available only for very advanced students in a very small number of elite yeshivas in Jerusalem. It goes without saying that I meet none of the requirements for this option. I would also like to have some rest from Hebrew and Israeli society by being at an English-speaking "ghetto". Besides, only ultra-Orthodox yeshivas for the beginners like myself are available only in English even in Jerusalem, at least to the best of my knowledge.
Last but not least, I simply love the specific English-speaking ultra-Orthodox yeshiva in Jerusalem where I spent about four months about ten years ago: Ohr Somayach. This is the place where I was first exposed to ultra-Orthodox Judaism and its philosophy. I still remember vividly the intellectual surprises I experienced there. I am so happy that finally I can study there again from next Tuesday, though only in the morning.