A good way to learn or improve your knowledge of a language is to spend time in a country or region where it's spoken. A week or two at a language school will help, but to become really fluent you'll probably need to spend more time abroad. Some language schools offer discounts to students who stay for longer, or have special long term courses. If you can't afford such courses there are alternatives.
You could try finding a job that gives you plenty of opportunities to use the language. Or if your native language is English or you're a fluent non-native speaker, you could teach English. Some English language schools pay for their teachers to have lessons in the local language, and some even pay for your airfare to the country. So rather than paying for language lessons, you could get them for free while earning money and acquiring useful work experience. Courses such as the Cambridge CELTA and the Trinity Cert TESOL provide intensive introductions to teaching English and are offered in many parts of the UK and in other countries.
Translation, writing, web design and similar work can be done via the web, so you could theoretically work anywhere, as long as you have a computer and web access. Such work could enable you to spend time in foreign parts learning languages while earning a living.