In what language(s) will you write the announcement? Only English? The local language? Two or three local languages? All of the above?
Your answer to these questions should depend on the level and requirements of the position. For example, it might be unrealistic to post jobs for lower-level positions only in English. In many countries around the world, only the highly-educated elite speak English, so you should expect that for low-skill positions (guards, cleaners) you will need to post the job in one or more local languages.
Some positions, on the other hand, might require very high levels of English. In this case, you might not want to post in any local language at all, helping you weed out candidates before the CVs arrive.
What is the literacy rate in the local population?
If a large percentage of the population is illiterate you should take this into consideration when announcing lower-level jobs. When national literacy rates are low, you may have no choice but to hire illiterate or semi-literate staff. And if you know you will need to do this, you might want to supplement print advertisements with radio or some other form of non-written communication about job openings.