Epernay LFSW - is it FR-only?

I’m looking to fly EBGB to Epernay LFSW but can’t find the airport in the eAIP listing here. Is that normal? Not sure if I’m looking in the right place.

Since it is a VFR-only airfield, it is not in the AIP strictly speaking, but in the Atlas VAC.

Also, on the LFSW VACs that google returns, the field is NOT listed as “French only” (eg this), contrary to most other uncontrolled fields I’ve seen so far in France.

Actually, the majority are not FR-only.

Does that mean English is OK to use?

Yes. However, it could still create some confusion as not all „French“ pilots understand radio calls in English.

My French is very good but I’m not a native speaker and I don’t have a French ELP, after spending countless hours reading discussion on the topic on this site I still can’t figure out whether that is mandatory (at least in theory) or not – would prefer not to leave any loose ends

French ELP does not really play a role here. It is being competent to make and understand radio calls in French that matters. But again, in this case, strictly speaking, you are fine with calls in English.

Take note that Epernay uses 123.5, i.e. the common frequency for smaller French airfields that don‘t have a discrete frequency. On sunny days, 123.5 can be chaos. Make sure you top and tail your calls with the correct airfield name, pronounced correctly, to avoid adding to the chaos. Also, listen very carefully to other pilots calls to make sure you get which ones are actually for Epernay.

Finally, on the above VAC under miscellaneous item 7. it says “Préparation du vol / Flight preparation : Acheminement FPL VFR / Addressing VFR FPL : voir / see GEN 12”. Do they mean GEN 1.2 regarding the filing of a flight plan?

No, GEN 1.2 is not about flight plans. No idea why they write GEN 12, which doesn‘t exist. It‘s ENR 1.10 and 1.11 that are about flight plans.

2 ways you can do this.
1/ download the SOFIA VAC app on either google play or the app store. That should give you all VACs but it seems to only work on certain mobile equipment. Mine says it is not available for my phone, but it is not exactly modern.
2/ If you go onto the SIA website, accept cookies and the push menu, you will have a list on the left hand side.
I think you might be highlighting.eAIP
That is mainly for text and Instrument approach charts. Instead go to the 2nd section down and press on Atlas VAC. That will bring up 2 books on the right. Press on the airfields one. The other is for helicopters. This will bring up 3 boxes. Of you don’t have the OACI (ICAO) code enter Epernay. 3rd box down will come up with the airfield"s full name. Click on that to put it on the top line and press ok. This will bring up the VAC and or download it to files
It sounds more complicated than it is in reality.
If it doesn’t say French only you.can use English unless the frequency isn123.5.
If you have enough French to be able to announce normal phraseology in French eg vent arriere (downwind) and étape de base ( base leg) don’t worry about it. Just don’t use English and you will be fine.

The VAC Chart for Epernay LFSW (all such charts are available in SkyDemon) does NOT state: ‘FR seulement/only’. Therefore the use of English is perfectly legal and allowable.
Whether, from the reaction of local French pilots in the circuit, you should continue to use English is another matter. To convert to using basic French RT calls as shown in this simple aide memoire will win friends in the Club House when you have landed:
french_rt_calls_pdf
Likewise, to greet Monsieur Le President in fleeting French is far more likely to get him to willingly use his Fuel Card in exchange for your Euros.

Frankly if your French is good, it’s safer to use French. Epernay is a nice, welcoming airfield, with some interesting aircrafts; but it’s fair (and not unreasonable) to say many local pilots will get a much better sense of what you are doing in the local language.