For documentation on hyphenation, read http://documentation.scribus.net/index.php/Hyphenation
Issues on debian
Debian's scribus 1.4.4 users regularly have issues with hyphenation in various langages.
Gabo describes how he sorted this issue (for spanish language) :
Under the preferences is the option to download some dictionaries.
I have to move the downloaded dict to /usr/share/scribus/dicts and /usr/share/hunspell (not sure which one is the correct location)
Also the /usr/share/hunspell was renamed to hyph_es_ES.dic just like the existing hyph_en_US.dic
FMartin (for Italian and Russian languages):
When I installed Scribus I only found Lituanian hyphenation. I needed Italian and Russian. You may try two options to solve the problem:
a) instal the hyphen_it package or hyphen_ru.
b) Italian: download the extension for Italian for LibreOffice (Tools -> Extensions Manager,...), extract from the downloaded file the file hyph_it_IT.dic (or hyphen_it_IT?), move it to usr/share/hyphen/
After that, it's mandatory to do a copy of the hyph_it_IT file at this same directory with the name hyph_it.dic After that, of course, choose the Italian language for the document and at the character styles. (Sometimes hyphenation in Italian doesn't work well, as in "no-stro", "ester-no", "aspor-ta-zio-ne").
Russian: download the extension for Russian for LibreOffice called "Russian dictionary pack" (Tools -> Extensions Manager,...), extract from the downloaded file the file hyph_ru_RU.dic, move it to usr/share/hyphen/
After that, it's mandatory to do a copy of the hyph_ru_RU file at this same directory with the name hyph_ru.dic After that, of course, choose the Russian language for the document and at the character styles. (Russian hyphenation works really well).
In 1.4.4, hyphenator uses the "Preferences" language, not the document language.
Fine tuning of hyphenation
If a line after the last line that features a hyphen has too large word spaces, you can adjust the hyphenation manually with soft hyphens (also called smart hyphens). You can use the menu entry insert > character > smart hyphen or its ctrl + shift + - shortcut. Or you can remove hyphenation locally. Select the text for dehyphenation and run Extras > Dehyphenate.
Also, If you want to squeeze some text, select it and set horizontal scale to 94-98%. This works with most text-sized fonts. A difference between normal and condensed script cant't be seen.
With 1.3.4 you can create manual line breaks, so that if the word starts with a soft hyphen, it does not hyphenate.
Further reading about Hyphenation in combination with Full/Forced Justification.
Detecting phrases left non hypenated
(In version 1.4.4) Even if we use automatic hyphenation, in some cases (copy and paste of a non hyphenated text into a hyphenated text frame), can result in phrases left non-hyphenated between others hyphenated. And looking at the hyphenated ones we can wrongly assume that all the text is hyphenated.
In Scribus there is no way to see if there are left phrases not hyphenated in the document.
An easy way to check it is opening the .sla file from LibreOffice. There we will see the characters included by the hyphenator to signal possible hyphenations (char decimal 173). And we will see if there is any phrase not hyphenated.