I was on a
Fairphone community meeting
yesterday and learned a few new tricks.
In order to not forget about them I write them down :-)

You may run into the situation that you want to use characters which are not
on the keyboard of the language you use normally. For me it is about Spanish
characters. Plus I want to have spell checking in English.

In order to do that, I go to Settings, select Language and Input, pick
Android keyboard settings and there languages.

First, make sure to disable the system language, so you can browse and activate
the languages to your heart likings.

When you are in input mode, that is, hit a text input field, you can switch
the keyboard by hitting the globe next to the space bar (several times, if
needed). This will trigger a change in the spell checking as well.
Sometimes, especially when my curstor was on a word, I had to hit the backspace
key once in order to get spell correction suggestions for the word under the
cursor.

By the way, you ought to be able to activate swipe input from the same settings
as well. Just don't navigate into languages under Android keyboard settings,
but swipe input. I haven't tested it myself, though.