Countries in English
Countries are part of our everyday conversations. How many times a day do hear somebody say "In Iraq / the UK / the US ..." and so on? At least several times a day!
As far as countries in English are concerned, you should know the words for one inhabitant, inhabitants (collective), language and adjective of a country. Most countries use the same word for adjective and one inhabitant (German, a German), except for a handful of countries (for example those ending in -sh — English, Irish, Polish, Spanish and so on).
Don't worry if you have used the wrong word, after all even native speakers make mistakes. For example, George W. Bush once said "Gracians" istead of "Greeks"!
The collective word for inhabitants of a country (demonym) is formed in these ways:
a) by adding the to the adjective form of a country (e.g. the Norwegian, the English, the Polish). This method is OK for every country.
b) by pluralizing the adjective form of a country with or without* adding the before it (e.g. the Norwegians, Hungarians, Germans). This method is not suitable for words ending -sh, -ss, -ch, and -ese.
* Of course, we do not omit the when talking about specific people, as in "the Hungarians (e.g. who we spent an evening with) were very nice people indeed."
Apart from that, the pluralized adjective comes with the if we're referring to the whole nation in a very general way. Please, express your opinion on that by adding a comment at the bottom of this page.
c) by using adjective + people combination (e.g. Iraqi people, German people, Italian people, English people). This method is OK for every country.
While in lots of cases all three methods give the correct words, you will sometimes find that one are less common than the others.
Lots of countries have more than one language. Usually the additional ones are the effect of colonization in that country (e.g. English or French in some African countries).