I haven't been using the LINE app with some Thais because it is so time-consuming: I only have a few chats going on, but they speak only Thai. This has been a problem on LINE as I had to cut and paste between Google Translate and the chats and couldn't read in English what I said or asked. There had to be an easier way to do this.
This has been solved by a nifty official LINE account called TH-EN translator. It does the translation automatically. You can install it by clicking on the "Add Friends" button and then clicking on "see all" of the Official Account Recommendations. Then click "Category" then "News/Tools" and scroll until you see TH-EN translator and add it as you would a friend by clicking on the icon and clicking the "Add" button. It will now be seen as a new friend.
To use, click the icon, then the down arrow and invite the user you want to chat with. It will create a new group between you, your Thai friend and the TH-EN translator friend. Anything you type in English will be sent to the other friend in Thai, but will retain your English text so you know what was asked or said.
I just found this today, so I am not an experienced user. I am probably the last to know about this, and you are all pros with this issue, perhaps? Also, my experience is limited to functionality on an iPhone. I don't know if it would work the same on other cell phones. I imagine if you can use LINE at all, you can install this. I am not sure yet if this works better or worse than Google Translate. I can't imagine the latter, but this is too useful a tool not to share right away, regardless. So if anyone has anything to add, or wishes to make comments, it would be welcome.