Most people use cheap Eurolites, which are just semi-transparent stickers. In the link below you will see how to position such a sticker on clear lens.
https://www.travel-spot.co.uk/products/eurolites.htmIt is perfectly possible to cut out such a sticker from a strip of wide masking tape, preferably of yellow colour and semi-transparent. The diameter of the Eurolites disc is about 7cm, but the best shape after adjustment turned out to be an oval 7x9cm. I've checked the masking tape solution on my "specialist equipment" (one device was me pretending to be an oncoming European driver and the other device was my gate) and it was just a little better than Eurolites, which are rubbish... There are three problems with the Eurolites: the beam is reduced, the shape is inadequate (see my note above) and the sticky part will leave marks on the lens. The masking tape solution does not have the last two problems, but it is still not good for night driving.
Beam benders, as Webcode suggested, are Fresnel lens and they are better (for example see the link below). They redirect the beam instead of masking a part of it. They will still leave permanent marks on the optical plastic and their focusing will be imperfect...
https://www.saxonind.co.uk/beambenders.htmSo, these are the options, which make me think that you will be avoiding night driving on the continent anyway. BTW, I've never heard of anyone checked by police on the French side, but i don't know about Austrians. Take some masking tape with you anyway -- it will help when the bought adapter falls off.
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