The DSM 7 package supports 8 languages at this time:
English, French, Spanish, German, Danish, Dutch, Chinese, and both forms of Chinese.
I can provide you with Czech translations of the instructions if you wish?
To use these other languages, change the DSM language
For PMS to work on DSM 7, you must either migrate from DSM 6 to DSM 7 or begin a fresh installation.
There is documentation (Screenshots) for DSM 6 → DSM 7 in this thread.
Also, it is best to download the latest from https://plex.tv/downloads
