I pondered on the word a while, for I recognized it from somewhere; Bosnia. I remembered hearing a Bosnian song and hearing a similar word mentioned in Bosnian.
Today over coffee, at the same café where I saw Tweezer Woman, I asked my Bosnian friend if she recognized the word istenem, and if it meant anything in her language.
Apparently the word for truth, is istina. I asked her if there was any word close to istina or istinem that in Bosnian meant God, just like it does in ancient Hungarian. She explained that the word for God in Bosnian (and Serbian) was bog (very similar to Russian & Ukrainian Боr and боr) , however in everyday slang God is referred to as Istina.
Apparently there is a Bosnian saying that goes:
Istina je samo jedna
tr: The truth is only "one"
Being a Muslim country as such, it must have incorporated the spirit of this meaning in everyday slang thus translating Truth into being synonimical to God. For just as there is only one truth, there is only one God.
Another interesting Holy Linguistics fact.