My German grandmother used to say "Yokas en Himmel" which she said meant "my god in heaven". I can find the word Himmel but not yokas - would like to know the correct spelling and translation of this saying.
In Swabian dialect, especially in rural regions, it is still today quite common to call
Jesses em Hemmel!
(both "e" are short) or
Jeeses em Hemmel!
(long "e", and sonant first "s") which would be "Jesus im Himmel" (Jesus in Heaven) in standard German.
(For alternative pronuncation Jekkes see below.)
Other common expressions are
Jesses Maria em Hemmel!
Jesses Maari ond Josef!
Not to speak of
Herrgott em Hemmel!
Herrgott Sack Zement!
where the last three are disguised forms of saying
I would suppose your Yokas en Himmel is related to Jeeses em Hemmel.
Jekkes is a form of pronouncing Jesses or Jesus that can be heard in some regions. I remember people saying Jekkes Maari, too.
All these exclamations are used to express surprise, either joyful or distressed, or anger.
As for spelling: German dialects (including Swabian) are not usually written. There is no convention on how to spell. Whoever decides to write dialect anyway (usually for humoristic reasons) chooses spelling as he or she thinks fits best. Note however, that "y" in German is never used as you do in English. The letter used for that palatal i-like transition sound is "j".
As for translation: this should be answered by a native speaker of English. Perhaps
It could be "Lukas im Himmel", which is something my great-grandma used to say on occasion, talking about the apostle, though, not god. It seems to be a pretty rare saying, I haven't heard anyone else ever use it.
My great-grandma lived in Saxony as an adult, but I do not know where she was born or grew up.