Simply translating the original keywords to the target language is not an appropriate approach. Some English words are, in some languages, more commonly used than the local equivalents, so they must be included in the keyword list. Also some super-up-to-date English keywords may sound outdated or odd in another language, even if the translation is formally correct. When choosing the keywords, the help of someone who is really in touch with the real language is invaluable.
Date, number and unit formats
A quick and simple tip but a real must; without these conversions the website looks unprofessional.
Language chooser option
Many websites redirect users to the localized version, depending on their IP address or the browser language, assuming that they are proficient in the language of the country from which they're accessing the website. Case in point: think of people living in a country with a language and even an alphabet they don't understand, usually for working, who are automatically redirected to a website they can't read. Give them a manual language choice at least, please.
Different languages for different countries
If you want to start a business in Canada, you can't ignore the fact that the country is actually bilingual and a French website must be coupled to the English one. That's not an isolated case: Switzerland, Belgium and India are just some other examples. If one country is crucial to your business, you should cover all its official languages. That may seem overzealous, but consider that in most bilingual (or multilingual) countries, the language belongs to the national identity which carries a very high level of importance.
Check hrefLang tags
It may seem strange, but regional codes are often misspelled. That's because most people typically remember the most used ones by heart, but if you check the official list, you will find some surprises. In fact, the right code for English in the United Kingdom is
en-gb and not
en-uk, as many people think (this error is so common that Google now accepts even the wrong spelling).