en el que
 

I thought it would be interesting to read some literature in Spanish, so I found a copy of Heinrich Harrer's book, Seven Years in Tibet, in Spanish: Siete Años en El Tíbet. I would have chosen some Spanish (or Central/South-American) literature, but I couldn't find anything for free, so that's what I have got for now.

I have succeeded reading most of the beginning, but I just can't get a part of a sentence right. This is how it goes: [...] y en Karachi aguardamos que llegue el buque de carga en el que hemos de regresar a Europa.

I have got a feeling of it: they are waiting for a cargo boat to arrive, in which they will return to Europe - but I would like if someone could come up with a better translation. I think it's the subjunctive, llegue, which annoys me. Why exactly is a subjunctive used here? Is it because that it is not sure that the boat will actually arrive? Also, why is the el used like that, in en el que? I can't seem to find it in any pronoun tables.

The word el is a relative pronoun. It stands for the boat. The subjunctive is used for the reason you gave. Your translation is great!

You've got the translation right.

aguardamos que llegue el buque de carga en el que hemos de regresar a Europa
We are waiting for the cargo ship to arrive, in which we are to return to Europe.

aguardamos = we are waiting
que llegue = for it to arrive. This is the subjunctive, since it's a future event and there is a possibility it won't happen. eg: (cuando tenga hijos = when I have kids) subjunctive.
el buque de carga = the cargo ship
en = in
el que = which
hemos de regresar = we are to return, we are supposed to return

For more information on "el que", look up "relative pronouns" in a grammar book.

el cual, la cual, los cuales, las cuales, el que, la que, los que, las que are all relative pronouns. They are all substitues for "que", and are used to specify the number and gender of "que". They are used as subject of a dependent clause, or as the object of some prepositions:

(subject of a dependent clause)
Voy en un barco, el cual es muy grande.
Allí está mi mamá, la que tiene la bolsa roja.

You could substitue "que" in both those sentences, but the way I said it is more specific. Also, for example, you could use "quien" in the second sentence as well, but it's less specific

(object of a preposition)
Allí está el carro en el que viajaré este verano.
¿Ya viste aquel hombre, el cual se agachó para levantar el plato?

"que", "el cual", "el que" can all be used interchangeably in the above two sentences. In the second you could also use "quien".

Thanks to both of you. I was now able to find it in my grammar books, and all of them contain lots of information on them. Your examples was brilliant as well, Tomisimo! I have always just used "que," but I should probably try using the other way as well, to be more specific.