We often forget that English is not the only language online, and that many other nations who speak a multitude of different languages also have seo needs.
According to Internet world stats the top 5 most spoken languages are distributed like so: 29.4% of users are English speakers, 18.9% Chinese, 8.5% Spanish, 6.4% Japanese, 4.7% French.
Translating content directly from English for example, will not be good enough because there are many nuances proper to each language. There may not be enough keywords in a particular language to allow for a full optimisation.
The local culture may not be the same as for English speaking countries, so the copy will need to be adapted to what they're used to, the same style and the right tone.
We sometimes forget but different English speaking countries have different spellings and words for things too, so these also need to be taken into account, although it is essentially the same language.
It is better imho to re-write the entire copy from scratch rather than translate it.
Google is the most used search engine in most countries, but there are also countries who prefer other engines, like Yandex in Russia (45%), and the Chinese like Baidu.
You might want to look into registering the domain in the country that you're targeting, and keep the local extension in the URL. The competitors will be different to those for the English version of the site for example. The link building will also be localised.
Social media is also affected as you'll have to target the sites that people are using in that country. For example in the US Facebook and MySpace dominate. In Brazil it's Orkut, in Russia V Kontakte, Thailand Hi-5...
I suggest using a fluent speaker of the language who is great at content writing, with a really good knowledge of the local culture and SEO.
There's a free ranking tool that will let you know how your site ranks in multiple languages here.