1.3.3066 Linux SendOwl version has bad encoding in the filenames of the translation files.
Propably because of the tar.gz format. Previous .zip releases worked fine.
Translations with bad encoding are not available for selection on the options menu.
See also Unable to expand RimWorld? (https://ludeon.com/forums/index.php?topic=54179.0) at the Support forum.
Mac also shows bad encoding in 1.3.3066 language files.
Despite showing (_____) in the language name field, the selectable translations such as Japanese work, Spanish for example is not available for selection.
Thanks for this report as well, I'll also have it looked at.