Question: I just read a question with answers about the letter *u* making the sound /w/ in *penguin* and *sanguine*. However, the word *language* was not mentioned. What is the explanation for the spelling of *language*?

Answer: 
Here is how the spelling evolved:
<http://www.etymonline.com/index.php?term=language>

Pronunciation note: Because of the mentioned varied origins of English words, you pretty much need to memorize which words with "gui" or "gua" have a "w" sound. And which ones don't. 

For example, "guarantee", "guard" "guest", guild", "guile", "guilt" "guillotine", and "guise" have no such sound; they have a simple "g" sound. 

Words from Spanish with "gua" tend to have the "gwa" sound (guano, guacamole, Guantánamo). Also language, which is from French. 

An then there's GUI, which stands for Graphical User Interface, and is pronounced "gooey"!

Good luck to you. Luckily, there aren't very many of these words.
Part of the problem of the differences and inconsistencies between spelling and pronunciation in English is that there is no central arbiter of what is "right" and what is "not right". France has the Académie Française and Spain has the Real Academia Española or RAE to keep things in some kind of order. English doesn't. 

The French and the Spanish both began government backed standardisation of grammar and spelling as from the 16th and 18th centuries. As late as 1989, French prime minister Michel Rocard appointed the Superior Council of the French Language to simplify the orthography by standardising and bringing it up to date.

This has never happened for English. As far as I know,there is no English speaking state whose government has tried to impose standards.

The spelling and pronunciation of "language" as opposed to the spelling and pronunciation of "guard" often cause problems for non-native speakers.

Fortunately for the job security of English as a Foreign Language (EFL) teachers, there are many other examples that can cause problems, as the poem below shows. I don't remember where I found it, so hat's off to whoever wrote it:  

I take it you already know  

Of tough and bough and cough and dough?  

Others may stumble, but not you,  

On hiccough, thorough, lough and through?  

Well done! and now you wish perhaps  

To learn of less familiar traps?  

Beware of heard, a dreadful word,  

That looks like beard and sounds like bird.  

And dead: it's said like bed, not bead  

For goodness sake don't call it "deed"!  

Watch out for meat and great and threat  

(they rhyme with suite and straight and debt).  

A moth is not a moth in mother  

Nor both in bother, broth in brother,  

And here is not a match for there,  

Nor dear and fear for bear and pear,  

And then there's dose and rose and lose -  

Just look them up - and goose and choose,  

And cork and work and card and ward.  

And font and front and word and sword,  

And do and go and thwart and cart -   

Come, come, I've hardly made a start!  

A dreadful language? Man alive,  

I mastered it when I was five!