Although English is the lingua franca of international commerce and may help you secure a job in some countries, the most important qualification for anyone seeking employment is the ability to speak the local language. If you don't already speak the local language well, don't expect to learn it quickly, even if you already have a basic knowledge and take intensive lessons. It's common for foreigners not to be fluent after a year or more of intensive lessons. If your expectations are unrealistic you will become frustrated, which can affect your confidence. It takes a long time to reach the level of fluency needed to be able to work in most languages and to understand the various accents. If you don't speak the language fluently, you should begin lessons on arrival and consider taking a menial or even an unpaid voluntary job, as this is one of the quickest ways of improving your language ability.
If necessary you should have lessons before starting a job. A sound knowledge of the local language won't only help you find a job or perform your job better, but makes everyday life much simpler and more enjoyable. If you go abroad without being able to speak the local language you will be excluded from everyday life and will feel uncomfortable until you can understand what's going on around you. The most common reason for negative experiences among foreigners abroad, both visitors and residents alike, is because they cannot or won't speak the local language.
However badly you speak the language, your bad grammar, poor vocabulary and terrible accent will be much better appreciated than your fluent English!
Further information is available in our Living and Working series of books.