How much is editing hard when cultures are different in the job area?

It's not that hard when you know both the cultures well and can find parallels between them. Even when you're editing a text on an unfamiliar topic, you can always do research or ask subject matter experts for advice. I think it's much harder for the writer/translator - the editor is just there to affirm their choices or come up with improvements. You mustn't be afraid of hurting the writer's feelings by making too many changes - it's your responsibility as an editor to make the text sound good. Respecting the natural flow of the target language while preserving the message of the original is the most important. Translating Arabic into English, for instance, is extremely difficult because not only the languages but also the whole systems of thinking are diametrically different. I have seen quite a few Arabic books which, although highly rated in the original, were not so enjoyable in English due to poor translation. In this case, good, fearless editing can make all the difference. If you're holding back on doing edits that you feel are required, you're doing a disservice to the author.

I have worked in India, for academic publishers outsourcing to India, in the Sultanate of Oman and. lately, Dubai in the United Arab Emirates. 

I find that cultures play a major role in editing.

In some cultures, some issues are considered culturally sensitive. For example, when editing in the Gulf region, any mention of alcohol is considered taboo along with a whole range of other issues that may not even seem worthy of consideration in other locations and cultures.

Editing is slightly more difficult when you need to keep all these issues in mind. And, there are only so many other ways of differentiating between beer, wine and champagne when you are writing about different menu offerings of restaurants, especially during Christmas and New Year.

Once these issues are clearly remembered, it is not so hard.

Editing is so simple providing that you know the technical side as an editor.

I believe editing can take care of the critical attention and refinement that will ensure your writing reaches the required standard. This means an editor does not need to worry about cultural differences if his job is to edit, and not to write the initial copy.

Not hard at all. Actually, it is only natural for a translator/ editor to work on texts from different culture. It is part of his/her job, as different languages most likely mean different culture to some degree. However, the translator should be proficient in both languages (source & target) and therefore familiar with both cultures. Again, just like Jana mentioned, the translator will be doing the most part.