Where Should I Go?

That is an open end question! Since she speaks a little French seems like France would be a good choice. And somewhat centrally located. How about Paris? Good transportation center. What is your budget. Find an apartment and move in. Where would she like to go????

London-plenty of air connections, great train system for many daytrips near London or longer trips to Scotland and Wales, Eurostar to Paris.

Centrally located for travel to other places? Madrid, Spain or Innsbruck, Austria

We just returned from Paris and it was very expensive and a hassle to get around on their metro. We found the Spanish to be very accommodating, and the price of travel there to be very inexpensive. There are other cities within close proximity, like Toledo, that make for great day trips.

From Innsbruck, it's very easy to take train day trips to Munich, Southern Bavaria, Salzburg, Northern Italy (Venice) and even Switzerland. It's in the center of it all.

Bologna, Italy. It is not a huge tourist destination (maybe that's why it's cheaper to stay there), it is centrally located and is a rail hub so it's easy to day trip to a lot of interesting towns and makes it possible to do 1-2 night trips to explore other places. There is enough variety in Italy that you don't need to spend time in other countries.

It's curious that you say "learn" - do you mean you want her to go to school? Especially since you also say "weekend adventures" implying that overnight trips on weekdays isn't on your radar. In fact, most overnighters are better during the week because a lot of locals go to popular places on the weekends.

I can't think of anywhere in Europe where you can't get along knowing only English - though knowing some French has helped me a lot.

How about Quebec? It's like Europe only more conveniently located.

Let's think about this. You want somewhere you can do trips from over a 3-4 week period.
You want a city that is a rail hub, and is an air hub for one of the cut price airlines.
You also want a city that it is worth spending many days in for the rest of your trip.
You want to be based in one location, that implies having this accomodation throughout the 3-4 weeks, and your trips are day-trips, max 1-2 nights (otherwise you are paying double for accomodation and it is worth moving out).
French speaking is an advantage.

I don't know where you are from so I can't put that in as a factor.
What are your and your nieces interests (old cities, architecture, countryside, history, mountains, walking around or being driven around?)
What time of year is this trip?
And what is your budget per day?

This is a map showing where Easyjet flies (the biggest cut-price airline). Any city with a lot of destinations is a good option: http://www.easyjet.com/en/routemap

My thoughts:

• Paris. Lots to see. But long rail trips to get to other good cities. As a Mega city, the airport takes a long time to get to, and mega-citiies for 3 weeks are not to everyone's taste.
• London - similar logic.
• Prague (or Vienna). good trips to Each other, Budapest, Bratislava, Berlin, Munich.
• Basel, where I live. Nice smaller city for looking around, train hub for Switzerland, SW Germany and Eastern France. Lots of flights from easy-access airport, but VERY EXPENSIVE.

Maybe Belgium? Maybe base in Antwerp? From there you could do day trips to Bruges, Ghent, Brussels, Mechelen and other locations in Belgium. Within easy enough weekend reach would be Amsterdam, Paris, Aachen, Maastricht, etc. Lots of stuff in between and extensive train service from there. Language is not an obstacle, or wasn't in our experience, anyway.

Give me the month you plan to travel and I'll give you a suggestion.

My suggestion would be Frankfurt. Major air and rail hub. Easy train ride to most of Germany, France, Belgium, Netherlands, Prague, Poland, etc. You have the Rhine and the Main river valleys right there, Wurzburg, Nuremberg, Koblenz, Koln, Mainz, Bamberg, Heidleberg, Luxembourg, Trier, Bonn; all of these are close by train. English is common, that wouldn't be a problem. Brussels, Paris, Amsterdam, and Switzerland are all direct by train, or easy hops by plane.

My other suggestion would be Vienna. From there you have Salzburg, Budapest, Bratislava, and Prague all within a couple hours on the train. It's also a fairly cheap place to fly into, and a really nice city to explore.

Make it simply --- hang a map and throw a dart. It is a great time saver.

Consider Toulouse, central southern France. Near rivers, mountains and the sea. And Spain is really close. French is a romance language and it helps with Spanish. Now, there is google translate.
Now, Frank! I threw my dart and it landed on a small community below Bolzano, Italy and it slipped to Dresden, Germany.

U do not mention budget so I am to deduce $is not a problem. I suggest London.
A fab city with loads of sights and world class museums. Easy day trips out to Oxford, Cambridge, Windsor etc. London is fabulous.

You could look at it this way: you don't know any foreign languages. Is that going to be an obstacle for you? Are you going to let it be an obstacle? Will this language "thing" deter from going on a trip to , say to Poland or Germany or to Czechia?

You could at it this way too: ...so what if I don't know any foreign language. I'll take one up, if not, I am going anyway.

My suggestions are going to France, England, Austria, Holland. No suggestions on accommodations since I don't use the apt, and AirBnB options.

Sorry, Bologna didn't do much for me.

So many choices.

A large city like Paris, London or Rome have much to see and do, but are more expensive.
If you pick a large city, you can stay in cheaper lodgings by finding a place away from the downtown and use bus or rail transportation.

The language issue has never been a problem for me. I had college Spanish but after years of nonuse, I can't do much with the language, still having been to 78 foreign countries, I never had a problem getting around where I wanted to visit.

Some of my favorite countries are Great Britain, Portugal, Italy, Australia and Japan. Also, loved South America (Peru, Chile and Argentina). South America is cheap and lots to see.

Southern Europe tends to be less expensive. Stay away from Norway and Switzerland if cost is an issue.

Augsburg, Germany (we lived there for 4 years) is 50 miles west of Munich and you can take the train into Munich or visit other places in Bavaria easily.

Italy is so filled with history, art and culture. Also, great food. Florence is the cheapest of the major cities.

Wow, this is like a blank cheque. So let's see, if you want to go for central areas, I think Germany would be a good option.
For a first trip to Europe, you need a good first impression and with its sights, people and price friendly cities, I honestly feel it should be the top on your list. Furthermore, with the amount of time you have, It's totally feasible to check neighboring cities. I mean, there are train tickets to Austria, Poland, Belgium, even France ( so your niece's french could be exercised there) and one of my favourite places Russia.
You can even take a Baltic cruise, that way you would be having twice as much fun and killing two birds with one stone: cruising and sightseeing. My Baltic cruise was so memorable, although I used a shore tours travel guide : Anastasia tours, when we got to St Petersburg. I really didn't want to spend so much time with the less intriguing sites and at the end of the day miss the more memorable sights or worse spend time in traffic because I didn't know the easier route or because a cabbie wanted to use me to make a little extra cash, gosh that woul have been annoying.
For the language, you can get away with English, though knowing some little phrases and words in German like the greetings would earn you points with the locals.
All in all, Irrespective of wherever you pick, just make sure you have fun.