MadCap Flare file type is built in Studio 2017 already.
Thing is that its default configuration includes only *.htm and *html files, while MadCap Flare produces way more filetypes with localizable content (flmsp, flsnp, flpgl, flglo, fltoc, flvar, fltar, flprj and god knows how many more).
You need to add all these to the configuration yourself, plus also add the corresponding root element names to the configuration, plus perhaps also add/edit the Parser settings to your needs.

Plus, very important thing: read this thread if your customized MadCap Flare file type will keep disappearing from the list: https://community.sdl.com/product-groups/translationproductivity/f/90/t/15217

You need to add file extensions of the other localizable MadCap Flare files, plus configure a way to recognize/detect them (in my examples I used their root elements):

(the last root element in the list, not visible on screenshot, is "CatapultProject" for the *.flprj MadCap Flare project files)

Then you might also need/want to edit the Parser settings to add/edit the XML parser rules according your requirements.
For example here you can see some added rules for the added *.flXXX files (the "//Variable" or "//Content" and other rules), a special rule to exclude texts set as "Do Not Translate" and "Under Construction" (i.e. draft) in MadCap Flare, or an extra rule to exclude texts in <code> element, per client's requirement.

And here is an example of some further finetuning:
- a rule to localize hyperlinks, but finetuned to extract link only if it contains a slash (to exclude zillions of nontranslatable links to in-page anchors like <a href="#hist_tags_anchor">hist_tags</a> and not pollute the files with useless stuff screwing up the wordcounts)
- rules to color texts with "class=uicontrol" attribute, and to color MadCap Flare tracked-changes texts... to visually help translators to comprehend the texts (which gets REALLY REALLY tricky if tracked changes are left in the file!)