Your assumption is correct, when a text message is received internationally, the message must be sent in English to of course be legible. Same concept if you ever talked or have seen a website based in another country, it will appear with symbols and characters that are unable to be interpreted by your computer unless you change the system settings on your pc. The downside is that there is no way for your actual phone to automatically interpret this language as your phone is built based around the English language. You could try some things online, but I'm almost positive there aren't many ways around this since the software on your phone is restrictive in terms of changing it's font capabilities. Also this interpretation of characters takes place through the switch, and therefore changing your device may not have any impact even if it were possible.
Sorry to hear about your troubles with this situation, but yes it is definitely something that becomes harder to manage as opposed to regular domestic text messages.
The text message will charge on your bill as long as it's reaching your phone, so simply ignoring the message will not prevent the charge.