One can definitely say simply “50 Euro” or “50-Euro-Schein”, but is there some sort of colloquialism like eine Fünfzig, analogous to a fifty in English?
Ein Fünfziger is very often used to refer to a 50 Euro bill (at least where I live), as well as ein Zehner (10 Euro), ein Zwanziger (20 Euro) and ein Hunderter (100 Euro). Another term would be Fuffziger.
I also sometimes hear the term ein Fuffi for a 50 Euro bill (but those are mostly on TV).
Fuffi is colloquial in some parts of Germany. These names were already used before the currency conversion from Deutsche Mark to Euro. Elder citizens might refer to coins in the same way they did at that times: Groschen (10 Pfennig, now rarely used for 10 cent).
Back when we had Schilling in Austria, I often heard and used the terms Zehnerl (10 Groschen) or Fünfzigerl/Fuffzgerl (50 Groschen) when referring to Groschen coins. Since the Euro, I haven't really heard or used those terms. I usually just hear "XX Cent" or "XX Cent-Stück".
Also in Austria you will hear »Fünfziger« for a 50 Euro bill. The same pattern is true for all bills:
- Fünfer (5 €)
- Zehner (10 €)
- Zwanziger (20 €)
- Fünfziger (colloquial also »Fuffziger«) (50 €)
- Hunderter (100 €)
- Zweihunderter (200 €)
- Fünfhunderter (500 €)
Before we used Euro, our currency in Austria was Schilling, and in those times we had bills with bigger numbers (but less value):
- Tausender (1000 Schilling)
- Fünftausender (5000 Schilling)
The word »Fuffi« is not common in Austria. I never heard it before.
There is the term »falscher Fuffziger« which literally means a fake 50 Euro bill, but is also used in the meaning of »insincere Person«. In this term you never say »Fünfziger«. As far as I know, this is true also in Germany.
In eastern parts of Austria there is a slang word for »Hunderter«, mainly used by shady persons: It is »Kilo«. This is interesting, because the greek word χίλιοι (chílioi), which is the origin of »Kilo«, has the meaning »thousand«. But as a thieves' cant word it has the meaning of a 100 Euro bill.
»Groschen« was in Austria the official name of the hundredth of 1 Schilling. So since we don't have Schilling and Groschen any more, we don't use the word »Groschen« for Euro-Cent or any other amounts of our "new money".
This question is lacking both an answer from the German and one from the Swiss point of view. I can provide the German, but I hope that somebody from Switzerland can step up for the Swiss.
As in Austria, all banknotes can be referred to by their value with a following -er.
5 € – Fünfer
10 € – Zehner
20 € – Zwanziger
50 € – Fünfziger
100 € – Hunderter
200 € – Zweihunderter
500 € – Fünfhunderter
1000 DM – Tausender (there is currently no 1000 € note).
Note that the way Fünfziger is pronounced will vary depending on where the speaker is from. Unfortunately, the Atlas der deutschen Alltagssprache only lists the variants for fünfzehn, so I didn’t include the map directly; but it is rather safe to assume that fünfzig will be pronounced similarly.
For coins is where it gets confusing. In the North of Germany, they will carry the same name as a corresponding banknote — this is explicitly excluding the 1 and 2 cent and 1 and 2 € coins. In the North, these usually du not have any specific name at all.
In the South, especially where Bavarian or Swabian is spoken, diminutives are used for coins of less than 1 € value — similar to their usage in Austria.
1 ¢ – Einerl(e)
2 ¢ – Zweierl(e)
5 ¢ – Fünferl(e)
10 ¢ – Zehnerl(e)
20 ¢ – Zwanzigerl(e)
50 ¢ – Fünfzigerl(e)
In Bavarian, the 1 and 2 € coins are also referred to as Iggl and Zwiggl respectively. Zwiggl seems to be a contraction of zwei Iggl. I cannot, unfortunately, provide you with any information on the etymology of Iggl. In D-Mark times, the diminutive Maggl was commonly used for the 1 Mark coin alongside Iggl.
Finally, the 10 cent coin — and its predecessor, the 10 Pfennig coin — are special cases, that are most easily explained with this map from the Atlas der deutschen Alltagssprache:
As you can see, in the North the terms Groschen and Zehner are used exchangeably, while the South uses variations of Zehnerl(e). Some Southerners will not understand you if you say Groschen — but most Northerners will correctly deduce what a Zehnerl could be.