lone, alone, solitary, lonesome

artur, can we say:
a lonely flower, a lonely desk, a lonely house, a lonely computer?

Well, excuse me, but none of the serious (paper and internet) dictionaries I've consulted (Collins, Hornby, Merriam-Webster, Cambridge online, Wordsmyth) confirms that 'lonely' can only refer to an emotion felt by humans (and possibly animals). These sources give other meanings, and at least one of them, glossed as 'empty of human presence, unfrequented, desolate, deserted, a long way from where people live' is common to all dictionaries.
Some of the examples given are: lonely house, village, hilltop, crossroads, stretch of highway.

So: lonely house - definitely yes (apart from appearing in dictionaries it is the title of a British novel and an American short story);
lonely flower - not usually; however, it suggests that for some reason we feel sorry for it or that the flower itself feels sad about its situation, which can be an acceptable metaphor;
lonely desk - a nice idea for a garage sale ad: 'lonely desk needs good home', but generally a less acceptable metaphor than above;
lonely computer - as above or something from '2001: A Space Odyssey'; this one obviously suggests that the computer can think and feel.

This meaning of lonely does have a literary or poetic ring to it, but so does 'samotny zagiel' in Polish. In normal Polish usage people are 'samotni' probably much more often than inanimate objects, too.

And, by the way, solaco33's example has 'porzucona na brzegu dnem do gory lodz rybacka jest tam rownie samotna jak bialy zagiel', so maybe the Polish author of these words meant to say something slightly unusual, and a slightly unusual word 'lonely' would express it just fine?

Personification - a stylistic device used in writing: attribution of human characteristics to animals, inanimate objects or abstractions

Animals, inanimate objects or abstractions are represented as having human characteristics (behaviour, feelings, character etc.). Personification can make a narration more interesting and lively.

" a lonely sailboat" would be perfectly acceptable

yes, I agree with you that 'Personification' as a device can be used in the literary sense. But analogically that would also mean that all inanimate objects can exhibit human emotions.
Next time you get in your car, talk to her nicely, tell her how wonderful she looks, how you're going to take her for a nice little drive.

As an aside, I talk to my plants and I know that they know exactly what I'm saying, they turn towards me and nod their little leaves. I tell them that I'm leaving them for a while, but that I will be back, they accept this reluctantly and when next they see me they shake with emotion and flowers open up as if to show that they are glad to see me.

You can avoid lonely's "feelings problem" and use just "lone"...

I have actually known quite a number of people (mostly men) who have "named" their car. Mind you, men have the strange habit of naming all sorts of "things". ;)