English may not be the most widely spoken language in the world (when it comes to the amount of actual people that speak a language leave it to the Chinese to outdo everyone...) It is however most definitely the language if business which is why it is important to have a decent translation service at hand, especially if English is not your first language.
When it comes to finding the right translation service there are a couple of things that you should be thinking about when comparing and considering translation services. The most immediate thing that comes too mind when thinking about translation services is whether or not the individual is qualified enough to give a decent translation and whether their translation can be relied upon. Generally speaking, someone with e a language degree should be able to help you and you should look at this as a minimum requirement.
Your alternative would be to find someone who has a deep understanding of both languages (normally this will be more experienced based people who might not have the paperwork but know how to do the job). These people should not be disregarded because they play an important role in the next factor that needs to be considered - that of cultural nuances.
We have all said things that come across as one thing and near another and with the diversity and far reaching impact of the English language, there is, all likelihood, no other language as guilty of this, what is polite in one culture could be enormously insulting in another and a few badly placed words could be the difference between your business being a success and a failure.
Ultimately, if you are looking for a decent English translation service, you need to bear both factors in mind - try and find a translator with the right qualifications (so that your work is always grammatically correct at least) but who is also a native to the area and can as such pick up on certain cultural norms which may be lost on others who are not familiar with the area. Think about it this way, there's a huge difference between Cape colored English and what is spoken in Scotland and if you had to get the same translator for both your grammar might be correct but that would be about it.