Northern Highlands is a region in Nicaragua.
If all you remember about Nicaragua is grainy footage from the 1980s of mustachioed men with automatic rifles, chances are, those images come from here. The inaccessible and rural north has been coffee country for centuries and a hotbed of political uprisings of all kinds for even longer. Augusto Sandino carved out a domain encompassing half the country from bases in this mountains in the 1920s and early 1930s. Fighting against - and beating - the US Marines, no less. After Sandino was shot by Anastasio Somoza, people disgruntled with the Somoza-led Guardia Nacional got themselves weapons and met in the mountains to plan the defeat of the Somoza regime. It was here that Carlos Fonseca founded the FSLN, or Sandinista party. It was also here that he was shot by Somoza's forces in 1976.
When the Sandinistas took over in 1979, disgruntled members of the Guardia Nacional and people who were disappointed with the new rulers got together and attacked the Sandinistas from bases in these mountains. At the same time, the Sandinistas struck back not only militarily but also by bringing new forms of (collective) ownership and a huge literacy campaign to these impoverished mountains. The literacy campaign (or "crusade" as it was known) was transformative for the teachers, not only the students. Many city-dwellers saw "rural" Nicaragua for the first time, with all this meant and many a marriage began in those days.
Today the area is mostly cleared of all remnants of its violent past - including almost all mines - and even though the hills and forests won't talk, they have seen quite a lot in the last few decades. Today the breathtaking nature, the coffee plantations where you can sample a cuppa on the farm where it is grown and of course the murals from the revolutionary era which you can find in towns all make this area well worth a visit. The region is also notably better at soccer than the rest of the country, where baseball rains supreme, with Real Estelí having won all national championships from 2007 to 2014.
This is the coldest part of the country and the cloudy forests are prevalent here (and are where all the coffee comes from). Consider spending a little more on your hotel if that little more gets you a warm shower as mornings are usually the coldest part of the day. Most locals get by just fine with cold showers, however.
Spanish. There are several language schools in Estelí and Matagalpa.
Buses to Estelí leave from Managua's Mercado Mayoreo. There is also less frequent direct service from Managua to Somoto, your best entry point to the canyon.
You can cross the border from (and to) Honduras here. On paper a treaty of free movement between Honduras, Nicaragua, El Salvador and Guatemala should enable you to cross the border without fees or permits, but in practice you will still be charged some fees in most cases. You should also not cross the border outside designated crossing points.
The famous Nicaraguan coffee that you have been searching all the time but just couldn't get? It is grown here and you can have a cup of marvelous black caffeine water around almost every corner.
Although this is one of the parts of the country where the Contra War hit hardest, it is mostly mine-free. If you should happen upon a place that is not, stay on the main road and ask your guides.