Both terms share their roots in the Classical Latin centenarius, meaning hundredlike, but the quintal has a convoluted etymology: It became Late Latin centenarium pondus, then in succession, Late Greek, κεντηνάριον (kentenarion), Arabic, qintar. The qintar was reimported to Europe by traders during the Middle Ages, where it became Mediæval Latin quintale, and finally Old French quintal before passing into the English language from French.
The word centner, on the other hand, is simply a Germanicized form of its original Latin name centenarius.
Languages drawing its cognate name for the weight from Arabic qintar include Spanish quintal, French quintal, Italian quintale, Portuguese quintal, Ukrainian квінтал (kvintal), Esperanto kvintalo. Languages taking their cognates from Germanicized centner include German Zentner, Lithuanian centneris, Swedish centner, Polish cetnar, Russian центнер (tsentner), Estonian tsentner, and Spanish centena.
Many European languages have come to translate both the Imperial and US hundredweight as their cognate form of quintal or centner.
Pound-based vs. kilogram-based
The concept has resulted in two different series of masses: Those based on the local pound (which after metrication was considered equivalent to half a kilogram), and those uprated to being based on the kilogram.
In Portugal a quintal is 128 libras or about 58.75 kg.
The German Zentner is pound-based, and thus since metrication is defined as 50 kg, whereas the Austrian and Swiss Zentner since metrication has been re-defined as 100 kg.
In Anglo-American countries
In English both terms quintal and centner were once alternative names for the hundredweight and thus defined either as 100 lb (exactly 45.359237 kg) or as 112 lb (about 50.84 kg). Also, in the Dominican Republic it is about 125 lb. The German Zentner was introduced to the English language via Hanseatic trade as a measure of the weight of certain crops including hops for beer production.