missing locale support

[Framsfex]

I have configured rustic with our locale S3 repository.
All commands seem to work, but the output is somewhat garbled, e.g.:

root@fex:/root/bin# s3rustic repoinfo
(...)
[00:00:03] scanning files...              â
[00:00:03] scanning files...              â ²
[00:00:03] scanning files...              â Š
[00:00:03] scanning files...              â ²
[00:00:04] scanning files...              â €
[00:00:04] scanning files...              â
[00:00:04] scanning files...              â
[00:00:04] scanning files...              â      â
[00:00:05] scanning files...              â
[INFO] using cache at /root/.cache/rustic/13e662d49a32a9e818867415d1a732b3e032f901717133bfabef33753d7dcb85
[00:00:00] scanning index...              ââââââââââââââââââââââââââââââââââââââââ         13/13
repository files
(...)

I suppose rustic does not respect locale settings:

root@fex:/root/bin# locale
LANG=POSIX
LANGUAGE=
LC_CTYPE=en_US.ISO-8859-15
LC_NUMERIC=en_US
LC_TIME="POSIX"
LC_COLLATE=de_DE.ISO-8859-15
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER=de_DE.ISO-8859-15
LC_NAME=de_DE.ISO-8859-15
LC_ADDRESS=de_DE.ISO-8859-15
LC_TELEPHONE=de_DE.ISO-8859-15
LC_MEASUREMENT=de_DE.ISO-8859-15
LC_IDENTIFICATION=de_DE.ISO-8859-15
LC_ALL=

My terminal has no UTF-8