A while back someone passed around a quote from the FireFox team that said something like "We should strive to ensure that every user, no matter what language they speak, can have a consistent experience with our product." The reason for sending it around was to prod the writing team to strive for the same thing.
I generally agree with the sentiment of the statement. Language shouldn't be a barrier to accessing knowledge or a software product. Documentation and user interfaces should be usable regardless of a person's native language. I won't attempt to argue what subset of languages are useful because that is purely a business/resourcing issue.
The statement got me thinking about the differences between making a UI available in multiple languages and making documentation available in multiple languages. I often hear translation used to describe both efforts, but I think that papers over a lot differences.
UI are not so much translated as they are internationalized. In general, making a UI available in a second language involves translating all of the labels and warning messages into a second, or third, language. So there is some translation being done, but it is fairly simple stuff. Most of the labels and warning messages are single words or short direct statements. It takes skill to be sure, but it is a pretty straight forward task.
Documentation really does need to be translated. In general, documentation requires more than a simple parsing of labels and direct statements into a second language. Yes, there are plenty of instances where documentation is little more than steps and reference tables which are just labels and short direct statements, but that is pretty low hanging fruit. I would also argue that simply because steps are short and direct that because they are part of a larger whole, they really should be treated as more than strings that can be changed without consideration of the context. With documentation, because it is a dense collection of language, you really need to consider the whole body of the work and translate it into a new language. This may mean rewriting parts of the content to be more understandable to speakers of the second language. For example, cultural references always sneak into content because they can help explain complex ideas. There are also structures like glossaries that don't always have direct mapping into the second language.
I have seen strategies for translation that attempt to stream line the process by treating the text like a collection of strings. It seems to the that while it may grease the wheels a little, it cannot produce truly good quality content. The systems all place a number of restrictions on the content originator to make sure the strings can be easily translated. Often it seems you end up with something that is mediocre in multiple languages, but is done quickly efficiently.
Wouldn't it be better to create great content in one language and then, if required, have full translations done. It may not be as efficient, but it will probably make for happier readers.