Language setting for 'TZD' format in TO_CHAR (timestamp with time zone)
You can get the TZD abbreviations with this query:
SELECT tzabbrev, tzname, TZ_OFFSET(tzname) 
FROM V$TIMEZONE_NAMES
WHERE tzname = 'America/Edmonton'

TZABBREV    TZNAME              TZ_OFFSET(TZNAME)
----------  ------------------  ------------------
LMT         America/Edmonton    -06:00
MST         America/Edmonton    -06:00
MDT         America/Edmonton    -06:00
MWT         America/Edmonton    -06:00
MPT         America/Edmonton    -06:00

I think they are fix and you cannot change it. Note, for time zone abbreviations there is no common or official standard, for every time zone you will find dozens of abbreviations, see https://www.timeanddate.com/time/zones/na.
If you need a language specific output you could use CASE or DECODE
DECODE(to_char(systimestamp at TIME zone 'AMERICA/EDMONTON', 'TZD'), 'MDT','HNR' ,'HAR')