It looks like the options.txt file is read and written using the default OS encoding. This can cause problems with resource packs whose name contains non-ASCII characters.
- Create a resource pack with a non-ASCII character in its name or download the attached §3MC-117449.zip and place it in the resource pack folder
- Select the resource pack
- Restart the game
→ The resource pack is not selected anymore. Additionally the options.txt file shows a malformed resource pack name ("Â§3MC-117449.zip")