Translation cost is not the issue here, the actual cost is the printing (more pages in more languages cost more, but then again, it also costs extra to print many kinds of different manuals). Deliberately leaving out for an example English (the US is usually not the origin country for imports) is. So:
1) Make sure you leave out English where it is not a major (first) language. Do the same for user interface. This prevents imports from cheaper countries in Asia.
2) If you want to prevent selling to neighboring countries select the languages appropriately. I have seen cases in Finland where an appliance sold in Finland includes manuals and UI translation in Finnish, Swedish, Norwegian and Danish, but the model sold in Sweden has for an example only Swedish, Danish and Norwegian or the other way around - this combined with selecting which markets you want to sell which model to you can easily create semi-artificial market segmentation.
The point with manuals is nowadays gone because nearly everything is available online, and even printed manuals are now largely universal (my latest purchase, an Onkyo home theater amplifier, had sections "US model" and "Asian model" when describing features), but sometimes manufacturers still play games with localization and target specific countries only with specific models, and buying the better price/value sister model from neighboring country may result in not getting the localization done for your country. You could argue that they are different products, but if the only difference is price, one letter in product number and you can get the translation back by flashing the "universal" firmware makes you wonder what is the real purpose of this "differentation".