UK: the British pound is the oldest circulating currency in the world, with a continuous history stretching all the way back to Anglo-Saxon times (over 1000 years ago). That being said, it has been reformed numerous times in the centuries since; the most significant coinage reform being the 1970 switch from predecimal currency (£1 = 20 shillings = 240 pence) to decimal currency (£1 = 100 "new" pence). You therefore cannot find any coins older than 1971 currently in circulation. Britain also changed numerous denominations since then, turning the 1p and 2p coins from bronze to plated steel, and shrinking the 5p, 10p and 50p coins. In practice, this means that the oldest coin you're likely to find in change is a 1982 20p coin, or maybe a 1971 1p or 2p. The older shilling and pence coins are never seen in change but any coin dealer will have bucketfuls of the things under the counter. Note: the 1 pound coin was the most recent reformation, in 2017. 1 pound coins older than this are no longer accepted in change.
France: uses euros. The French franc, the currency used prior to the euro, is now completely invalidated and cannot be redeemed for euros or any other currency, under any circumstances; this effectively means that pre-euro coins are now only worth scrap metal value, whatever that may be. Coin collecting does not seem to be as popular in France as it is in America, Britain, or Germany; I don't know how easy it is to find a coin shop there.
Germany: uses euros. While you won't find the pre-euro currency (the mark, or deutschmark) in circulation, unlike the old French franc, the old German deutschmark is still legally exchangeable for euros at any bank at the original conversion rate of 1 euro = DM1.95 - which means that German coinage has "retained" it's face value and is generally worth more than scrap. Coin collecting has a very long tradition in Germany and finding coin dealers generally isn't too hard. German coins - both pre-and post-euro - are all mintmarked, as Germany is the only country in Europe that maintains a multiple-mintmark system for circulating coins. There are currently five operating mints, with mintmarks A (Berlin), D (Munich), F (Stuttgart), G (Karlsruhe) and J (Hamburg).
Switzerland: the Swiss franc is the third-oldest non-reformed currency in the world; there are only three countries in the world where it is still theoretically possible to find hundred-year-old coins (including silver coins) in change, and Switzerland is one of those countries (the other two being America and Canada). However, many of the older Swiss coins were made of either silver or pure nickel, and the Swiss government and banking system has been very efficient in withdrawing, removing and recycling these high-metal-value obsolete coins from circulation, so the chances of a tourist finding a silver coin in circulation are virtually nil. Swiss coins are, as noted above, "very boring" in that they haven't even changed designs in over 100 years; this fact no doubt contributes to a general lack of interest in coin collecting in the country.
Austria: uses euros. The pre-euro currency of Austria was the schilling. As with Germany, schilling coins and notes can still be exchanged for euros, at a rate of 1 euro = 13.76 schillings, but I think you might need to travel to the Central Bank office in Vienna to do it. Still, their value is retained compared to French coins. I don't believe coin collecting is as popular here as it is in Germany.
The Eurozone: there has been a surge of interest in coin collecting within the Eurozone, as euros freely circulate throughout the Zone - meaning that it's perfectly normal to find Spanish, Italian, French or Dutch euros circulating in Germany. The three euro-issuing microstates - Monaco, San Marino and Vatican City - all issue tiny numbers of coins, with permission from the European Central Bank, and their coins have attained truly astonishing prices for circulating coins, given the small allocated mintages and the strong Europe-wide demand for their coins. The chances of finding one of those in change, though, are truly lottery-winning odds. It can sometimes be difficult to determine the country of origin of the euro coins, as they all have common reverses and the country of issue is not always named on the obverse - some just use a monogram (such as RF for France and RI for Italy) or just a portrait of the monarch, with the monarchs monogram (eg. Belgium). Greek coins are, of course, in Greek.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis