The province, as the rest of Belgium is a very safe place. However, some fights might occur at the end of villages 'bals' where heavy drinking is involved. However, those happen usually between local youngsters, and basic precaution will avoid any trouble, and you will find your stay a very peaceful experience.
French is the language spoken everywhere since its imposition in school. Nevertheless, a number of traditional languages are still spoken or understood by part of the population, especially in most rural areas:
The Ardennes version of Walloon, in the Ardennes
Gaumais in the south
Luxemburgish, a germanic language, closely related to German, with several French loan words, near the border
Dutch is spoken in most tourist places in the north of the province, because of large numbers of Dutch visitors during the summer. But even though most Belgians will have learned Dutch at school, you'll be better off with English in areas less used to tourists. Most young people will have at least basic understanding of English, and you should be able to sort out most things with it. German is spoken by some, especially near the Luxemburgish border.