Concerning the second question, Blažica & Lewis detail their method of translating SUS to Slovenian in their paper A Slovene Translation of the System Usability Scale: The SUS-SI. They use method of back-translating and psychometric evaluation to validate the translation.
There were three stages in the translation process. First, 10 reviewers from the fields of computer and natural sciences individually reviewed a draft translation. Second, the final translation incorporated their comments. The third stage was to perform a back-translation. Three independent translators, without reference to the original, translated the final draft back into English. The translators were native Slovene speakers fluent in English. For all 10 items, all three translators provided back-translations with the same meaning as the original and, in some cases, exactly the same wording. For example, Item 9, “I felt very confident using the system,” was back-translated to “I was very self-reliant when using the system,” “I felt very confident using this system,” and “I felt confident when using the system.”
Translated SUS was then used to test Gmail with 182 subjects who also provided the likelihood-to-recommend (LTR) score to be used with validation. Results were then analysed as followed:
- Reliability: assessed using coefficient alpha
- Concurrent validity: correlation between SUS and LTR
- Construct validity: two-factor solution of the SUS
- Normative comparison: comparing results to evaluation of Gmail using English language SUS.
For the first question I recommend the book Quantifying the User Experience by Lewis & Sauro, in which they present and compare different post-study and post-task standard questionnaires. They don't address the issue of this question but other post-study questionnaires to consider instead of SUS are UMUX with four items and UMUX-LITE with two items.
If you don't have to use post-study questionnaire, SEQ (Simple Ease Question) is a recommended post-task questionnaire and quite easy to translate. It just asks how difficult the user thought the task was on seven step scale and it could be asked by the person conducting the user test.
If you can't get your hands on the book, I'd recommend Sauro's website MeasuringU, if you haven't already checked it out.