I have translated prisoner into German in more dictionaries. I have four translations in total:
- Häftling (m)
- Gefangener (m)
- Strafgefangener (m)
- Sträfling (m)
Are they all synonyms?
They are all related to arrest but may have slight differences in the meaning:
means a person who's under arrest.
may either mean somebody who has been captured or arrested (during war: a war prisioner) or somebody who's under arrest (for whatever reason). So "Gefangener" could also be a captive or hostage, somebody who has been jailed or imprisoned for example by a criminal...
Is somebody arrested because of a committed crime.
Is a synonym of "Strafgefangener".
The words you are asking about can be grouped into two classes: one being Gefangener and its compound fom Strafgefangener and the other being those ending in -ling.
This is basically a nominalisation of the participle gefangen and means somebody who is captured. Intrinsically, there is no mentioning who (or what) captured him, how he is being captured/restrained and where he is — there is just something there that is restricting his freedom. Of course, this applies generally to everybody in jail but it is also used as a much more general term. For example, you could just have fallen into a trap or the restraining could be an entirely mental thing.
Als der Käfig von oben heruntersauste, wusste ich, dass ich jetzt Gefangener bin.
Er könnte es tun, will aber nicht. Er ist Gefangener seiner Moralvorstellungen.
Beim Sturm auf die Bastille wurden nur wenige Gefangene befreit.
As stated above, this is merely a compound word and the first component Straf- does nothing more than clarify that capturing is a punishment. At least, that is the theory. In practice, this word has become the standard and ‘official’ German German word for prisoner (see its Wikipedia entry). As such, it is the most neutral but also the most technical term for a prisoner.
Der Strafgefangene verbüßt eine Haftstrafe wegen Körperverletzung.
This word wasn’t mentioned, but it bears being added due to its similarity to the case above. The component Kriegs- of course means war, so this person is a prisoner of war. The rest applies analogously.
Both of these words include the suffix -ling. In some cases, that suffix has a pejorative function; in all cases it may be perceived as condescending (possibly from a higher moral point of view). Neither of these two words is fully in official usage but both are understood everywhere and used colloquially and in not quite as formal and official settings (e.g. newspaper articles).
This noun derives from the term Haft. Haft is an umbrella term for a number of different imprisonments with the sole common element of following a judge’s decision. Different types of Haft include Untersuchungshaft, Beugehaft and what is typically known as Freiheitsstrafe. In order of appearance these are remand, jail due to contempt and standard prison sentence. No distinction of the type of imprisonment is made in the word Häftling. (Note, however, that before a warrant has been issued the person is festgenommen, not inhaftiert and thus does not qualify as a Häftling.)
Der Häftling wartet jetzt auf seinen Prozess.
Wegen Körperverletzung werden Sie ein paar Monate als Häftling verbringen.
Weil er seine Schulden nicht bezahlen wollte, wurde er zum Häftling.
This one is a bit of an odd one out. It does not require imprisonment; however, it’s root Strafe requires conviction. Technically, a Sträfling could also be someone who has only been fined or to somebody convicted but not yet imprisoned, but in common usage it is mainly applied to Strafgefangene. Thus, most Sträflinge are Häftlinge but not all Häftlinge are Sträflinge. (However do note that this distinction is not always made.)
Der Sträfling muss drei Jahre absitzen.
Und so wird aus einem (Untersuchungs-) Häftling ein Sträfling.