I regularly attend Mormon services in both English and Spanish. My native language is English, and I did not take a real Spanish class until January 2012, when I was in my twenties. I had only taken Spanish 101 when I started going to Spanish Branch (branch being the word Mormons use for a small congregation), and it was a difficult (albeit fascinating) experience when I started going.
Spanish church building
Sacrament meetings in Spanish
Mormon services for the English and Spanish congregations are three hours each. Where I live, they begin with sacrament meeting, where we sing hymns, take the sacrament, and listen to talks from members of the congregation. I was able to sing hymns in Spanish from day one, but it was not until later that I passed or blessed the sacrament in Spanish Branch. Listening to talks was (and still is) a difficult endeavor, where there is much I don't understand, but my Spanish certainly gets better from listening to native speech. Sometime I'll have to listen to native speech in secular contexts as well, so I'll have secular vocabulary.
Sunday School room
Sunday School in Spanish
After sacrament meeting comes Sunday School, where the instructor teaches, asks people to read from the scriptures, and leads a class discussion (often with questions suggested by a teaching manual). I was able early on to understand Spanish well enough that I could tell which chapter and verse they wanted me to read, and I would read aloud in Spanish from our scriptures. This I was able to do well, because I read aloud from the scriptures three or four nights a week, in my reading of the Book of Mormon in Spanish. Understanding the questions and participating in the discussion was another thing, and only rarely have I answered a question in Spanish Sunday School; but it was nice to hear others read aloud from the scriptures, and hear native speech that I could simultaneously listen to and read.
Elders' Quorum room (same room)
Elders' Quorum classes in Spanish
After Sunday School, the adult men in the Spanish Branch would go to Elders' Quorum, and that was where I went during the last part. Each Elders' Quorum meeting would begin with a hymn; and since they had no piano or organ player, I volunteered to play. It was difficult to play and sing in Spanish simultaneously, particularly when the Spanish translations of familiar hymns had more (or less) syllables, and consequently more (or less) notes; but I was the only one who could play piano or organ, so I performed this service while I was there, so I could contribute to the meeting.
Teachings of the Presidents of the Church manual
The benefits of having a manual to read along with
Sometimes the lessons for Elders' Quorum would be out of the Teachings of the Presidents of the Church manual, and I could read aloud from the manual or hear others do so while reading along; but often times, the class members had no written material to follow along with. In these situations, I was (and sometimes still am) lost when hearing the teaching and class discussion; but my Spanish still gets better from listening to native speech. Again, I am only rarely able to participate in the discussion; but it has been known to happen occasionally.
Singles Ward church building
Going to English-language meetings afterwards
After Spanish Branch, I would go to my English-language meetings at our singles ward (a separate congregation for young single adults in the area), and I would be able to hear in equivalent English meetings what language barriers had prevented me from understanding in Spanish Branch. This made for long Sundays, but they were also very productive and enjoyable Sundays, and I learned a lot of religious doctrine by doing this, in addition to gaining the secular benefits of increased proficiency in Spanish.
The value of foreign-language services in improving proficiency
So that's a little about going to church in a foreign language. I highly recommend it to any religious people who want to improve their proficiency in a locally-spoken second language.
My experience with Spanish
My interest in foreign languages