My French is a bit rusty but here goes.

In response to your letter concerning the speed records that must
be affixed to trucks and caravans UK, circulating
France (Article R.413-13 of the French highway code), I can
make the following answers:
The Vienna Convention of 8 November 1968 deals with international traffic.
The principle was that vehicles in international traffic shall conform to the rules in its country of registration.
In practice we see the heavy-weight foreign travel to France with their own speed records.
The heavy-weight French abroad do not change speed records at the border to accommodate the country traversed.
But in any case, it should respect the rule that applies maximum speed on the road where it circulates.
Hope that answers your question and cordially,
The office of legislation and regulation
Delegation to the safety and traffic flow
Ministry of ecology, energy, sustainable development and the sea