Hi Hela,
Would you please tell me what's the difference between the words "barbarism" and "solecism" ?
For questions like this, it's usually good to look at the historical origins, the roots, of the terms.
barbarism The roots of this word relate to 'foreign speech'. The idea is basically that foreigners speak poorly, so a barbarism would be some way that a barbarian would misuse the language of civilized people. Barbarisms often result from what purists consider to be using a word in an improper way.
Someone who produces a 'barbarism' is considered to be someone who cannot be expected to know any better.
solecism The word is derived from the name 'Soloi'. The Athenians spoke excellent Greek, but they all believed that Athens's colony at Soloi spoke terrible Greek, with awful grammar.
Someone who produces a 'solecism' is considered to be someone who, really, should know better.
Would you say that a sentence such as "My mother seems has grown young again" is an example of solecism ? (= pure nonsense ?) No, not at all. There is a minor grammar error, but the basic meaning seems rather beautiful, quite complimentary to the speaker's mother.
Best wishes, Clive