COUNTRY SPECIFIC KEYWORD TERMS
This is a major source of keywords to discover. A good example from my own experience was the discovery of the keyword backyard that substitutes for garden in many situations in the USA. On the other hand it is hardly ever used in this gardening context in my own country and most other English speaking countries.
Another example of such a country specific term used often by English-speaking people in South Africa is the word veld which is an Afrikaans word meaning field literally but is also used as a synonym for countryside, open spaces and so on.
To discover these find a magazine (on or off-line) on your topic relating to the country you are targeting. You would also use this technique to discover terms peculiar to a niche topic.
You have probably used Googles search within results tool. Take advantage of this tool as follows.
Where do you live?
Lets say you sell fly fishing rods and your website is not designed to be well ranked for this keyword on an international basis. However you do want those visitors in your own region because you are really not able to deliver further than 50 miles from your home town. You must make sure that these web visitors all see your site.
This is accomplished by making sure that the name of your town, region is on your web page. Once is possibly enough. You will probably rank number 1 for searches on fly fishing rods + wigan where Wigan is the name of your local town.
Most designers do not use this simple but effective technique. Put your town/region on every web page, along with anything else of this special or unique nature when it makes sense to the visitor and the search engine to do this.