"Whose bread one eats, that person's language one speaks."
Translation:Kies panon oni manĝas, ties lingvon oni parolas.
German has a variation on this as a proverb: "Wes Brot ich ess, des Lied ich sing" = Whose bread I eat, that person's song I sing = I will do things that please the people who support me financially or on whom I am dependent. So if my boss tells me to jump, I say "How high?".
It also reminds me of the principle "cuius regio, eius religio" (whose region, that person's religion) where the religion of the local duke was automatically the religion of the local farmers that lived on the duke's lands, and if the duke changed religion (e.g. converted from Protestantism to Catholicism), the tenants had to do so as well.
This seems like an attempt to make an Esperanto-relevant proverb out of them, saying something like "if you grow up in a household speaking a certain language, then you will also speak that language" or something like that.
I understood it as being about the whole deal where the languages of the most powerful countries become "world languages" and many people disband the language of their own (smaller) people and rather just learns the dominant language in the region because that is the one which will get them jobs (bread).
And thus a very relevant proverb for Esperanto's (at least initial) goal.