Depending on your cpu overhead this may or may not be necessary. If you need to transact in other codecs Asterisk will likely transcode and increase the cpu usage. If you move a recording into your PBX using the system recording module, you can transcode into the different codecs that FreePBX offers at the time of import.
and extract to your correct language directory, many formats, quite a few languages, you need the ‘core’ sounds and the ‘extra sounds’ for completeness
Thank you for all the answers. Unfortunately my language is not provided there but I found it in the named format.
So if i understand correctly I can convert the sln16 files by uploading it via webinterface (Sound languages module) and then selecting the codecs I want it to be converted into like shown in the wiki: https://wiki.freepbx.org/display/FPG/Sound+Languages+User+Guide
No run time transcoding of the sound files will be needed if you pre-transcoded them into all those formats. Run time transcoding may be needed for other reasons, like recording calls, whispering, conferences, in band tone generation, silence detection, in band DTMF decoding, etc.
You will need slin16, not slin, as the starting point, to achieve the theoretically best results from G.722, but you did say slin16 in the original posting.