I just met a friend who has returned from teaching English in Myanmar. He loves it, he loves the students, he loves teaching, he loves Myanmar and he loves the new experiences. BUT, learning to speak the language there is very difficult. He is very thankful that there are English speakers who can help him.
When I was in elementary school I was taught Spanish, Peruvian Spanish (there are many varieties), and taught in Spanish. It was fun … because I was in elementary school and I didn't have a lot to do except go to school and play.
When I was in high school I went to Germany to work for a summer. I went on a boat and none of the men on the boat spoke English. I had to learn German and fast! When I got to Germany I worked in a small village and nobody there spoke English. I had to speak German to live! It was fun … because I was in high school and I didn't have a lot to do except go to school and play.
When I came to Japan I knew a bit of Japanese … but not as much as I thought I did! I had to learn fast! It was fun … because I was teaching English and I didn't have a lot to do except go to school and play.
I could have studied Spanish or German using an English text and when I needed to later, I did. BUT I couldn't use a Japanese text to study Japanese. It is too different. I had to use a book ABOUT Japanese written in English.
Whatever tools work for you are the tools to use!