Now they do have songs in English (including the most recent/popular ones), also in Chinese and like the other anon said in Korean too. But most of the tablet is in Japanese (except the part that takes you to the "languages" page where you can choose if you want the above mentioned ones). I have also noticed a new addition to the language screen tho, that now you can search for popular japanese songs in romaji and they will show you the lyrics in romaji too. Also these have three tabs : popular japanese songs/ anime/ and something else I cant remember because I'm a filthy weaboo and just kept choosing the anime one for easier searches lol
My absolute favourite karaoke chain is called "Uta Hiroba" (hard to miss, they have a smiley face on their title). The reasons are that 1) they are the cheapest (always a good reason tbh), and 2) with the price you get free all you can drink soft drinks, which in some places also includes slushies and ice creams.