I have been doing ebay for years, but I only do English websites. I really don't know those languages on other websites!
Don't know how to write the title and details? How to promote it? How to do customer service?
So language is really important. You can also learn about the market situation.
If you want to learn the operation and loading of eBay, I can teach you a thing or two, which is not very professional, but the basic operation and operation are still familiar.
There are many training institutions, but the fees are theoretical, and practical training is more expensive.
All by yourself, I have encountered all the pits I should encounter! So I can tell you what a pit is and how risky it is. Try not to go into the pit I've been in and spend money improperly.