Go here to learn more about translating.

When launching a Java simulation, some characters from non-English languages will show up as empty squares when the proper fonts are not installed. These links are instructions to install additional language support for various operating systems: Windows, Mac.

The embed code that is provided on a sim page points to the English version of the sim, but it is easy to modify the code to point to a translated version by changing " _en" to the desired locale (example: "_es_PE", "_hu").