"That is good, as long as it is true."
Translation:Das ist gut, sofern es stimmt.
Without any context, 'wahr sein' should work, too. Please note: you need 'sofern es wahr ist'.
I don't really understand why sometimes after conjunctions like these the verb goes to the end, and why sometimes it is inverted with its pronoun. I put "Das ist gut, solange stimmt es" as a previous example had had "Entweder gehen wir oder. . ." Can anyone help?
Some conjuctions send the verb to the end of the sentence. These are called "subordinating conjunctions". You can find a list of them here: http://german.about.com/library/weekly/aa010910b.htm
Das ist gut, solange es richtig ist. Would be my preferred and natural translation.
My translation was "Das ist gut, soweit es stimmt." and it was incorrect. Is "soweit" not the same as "sofern?"
"Soweit" is more like "as far as," while "sofern" is like "provided that." And I dont know that you would really say "That is good, as far as it is true." Another option instead of "sofern" would be "solang".
I am pretty sure german people will not bother about differences between "soweit", "sofern" or "solang", as they all contain "so" and "far", which means 'as long as' or even 'in case' (falls, wenn).
I am curious as to why "Das ist gut, solang es treu ist." is incorrect
"Das ist gut, solang es treu ist." this is not spot on, it means here faithful/trusty but not true, except otherwise implied through context, which is not given.
I would expect the following sentences for the meaning you imply.
Es/alles is gut, sofern du treu bist/bleibst. All is fine as long as you are faithful/trusty.
Other German examples:
Das ist gut, solange es richtig ist. "That is good, as long as it is correct."
Das ist gut, solange es wahr ist. "That is good, as long as it is true." (also logically true)
Das ist gut, sofern es stimmt. "That is good, as long as it sums up."
"Das ist gut, solang es treu ist."
It may work if you think "es" is your pet, and "das" is something you have talked about before about this pet. But I would not expect "true" in the English sentence but: faithful/trusty/loyal/devoted.