Translation:I think I will probably go to the party tomorrow.
In English, "I think I'll go" and "I'll probably go" have the same uncertainty nuance to me. "I think I'll probably go" seems odd to say, but can see it being said to add even more uncertainty. Is this the same uncertainty nuance in Japanese? Is both the たぶん and 思う together really adding more meaning here?
It is my understanding that the usage of 思う in scentences is often used even when the speaker is sure of what they are saying. (This scentence may be a case of this. I am not 100% sure.) This is due to the improtance of humility in Japanese language. For instance, I have listened to multiple Japanese who are very experienced in their feild, and they have all used the と思います form rather than です even when stating things they are sure of. Basically 思う is not only used to show uncertinty, but more so just as a way to soften ones speech as です and other forms can come off too assertive. Please let me know if I am incorrect. I hope this helps.
I THINK and PROBABLY together? Isn't there enough probability contained in I THINK already? Logically it would be either "I think I'll go..." or "I'll probably go..."
Don't you think so?
As it is now it strikes me as a poor... let's say: expression (no matter in what language - kind of like 'watery water' or 'smart genius' (or, more likely, the opposite of the latter)
I'm getting the impression that there are a lot of parties going on in Japan! Culturally speaking I wonder if that's really the case?
多分 means perhaps or probably. Your poor database is almost discouraging. Please update it or get a better Japanese /English speaker.