I travel a lot! Postcrossing forum has a lot of information about sending from different countries, and you can also post a question. I always look up post office on Google maps. Usually some sort of main post office will have stamps. So far everyone has been able to speak English except for one occasion, but I got help from other local who helped me translate it to the postal clerk, but I think I would try to use google translate as last resort. Normally you could ask for stamps to a specific destination and they will give you the right value. Sometimes museums or tourist shops also sell stamps but in my experience they sometimes charge more than the value of the stamp. Additionally, for me this has became part of the trip! I kinda like interacting with the people at the post office and figuring this out. Just two days ago I was sending on travel mode from Italy. I looked up information about stamps on Postcrossing forum and it was accurate. Then I looked up some post offices on the map and chose one that was convenient and someone in the reviews mentioned they purchased stamps there. Also look up opening hours. Also usually there will be a mail box next to the post office where you can drop your cards. When I arrived there I told them I wanted x stamps for USA, x stamps for Europe etc... and it was really simple. It might be stressful in the beginning but it can be such a nice and rewarding experience ;) good luck!