When you say you cannot continue, what do you mean? Exactly what happens after you click OK?
There is no Swedish translation available, so RealFlight should display that message just one time, fall back to English, and continue functioning normally.
You can manually edit your RealFlight.ini to make the error message go away, but depending on what else is happening it may or may not solve your problem. To change the language from outside the simulator:
- Go to the <Documents>\RealFlight 9 directory on your disk.
- Open RealFlight.ini in a text editor.
- Search for "Language".
- Change "Swedish" to "English". The complete line should look like this: "Language=STRING:English"
- Save the file.
- Run RealFlight.
Assuming you continue having problems, the next thing you could try doing is deleting RealFlight.ini completely. Or better yet, rename it to something else, in case you want to restore it or otherwise refer to it later on. This will reset all your settings, etc. to default. That may solve whatever is going on. Note that it will likely lead to KEError 55210 again the first time you run afterward.