In a bicameral legislature, is the first house the lower house and the second house the upper house?
The key thing is that there is typically a single house of parliament to which the government is responsible and that house has the most important role in the legislative process (e.g. it can overrule the other house in some or all matters). In English of French, it's called the “lower house”. But there are exceptions (including, of course, systems in which the government isn't responsible to the parliament at all).
The “first house” terminology seems less common in English and less consistent. The Dutch “eerste kamer” is definitely an upper house and in German too, “erste Kammer” is typically used to designate an upper house (alternatively called “Oberhaus”, which literally means “upper house”). Beyond the terminology, you have to look at the details of the system to figure out which is which.
My answer was EDITED to correct a mistake in the first version, I somehow got them mixed but the German and Dutch terminology are actually similar.