Can you please tell me if the following sentences were written by a native speaker? Thank you, Writeacher.

1) The usefulness of the study of languages is due not only to the frequent political and commercial interests, but also to the increasing number of jobs which require a knowledge of at least one foreign language.
2) This linguistic enrichment makes a determining contribution to the greatest possibility of cooperation.
3) Today, considering the difficulties faced by young people in finding a job at the end of their studies, better possibilities of studying languages would help solve the problem of unemployment, which is particularly serious in the industrialized countries.

1 -- definitely

2 -- maybe, but I'm not sure -- it's quite vague and "airy"!! (1 and 3 have actual specifics in them.)

3 -- maybe, but I'm not sure. The word "the" in front of "industrialized countries" is not usual for a native English-speaker.

In order to determine if the sentences were written by a native speaker or not, we can look for potential errors and evaluate the sentence structure and word choice. Let's examine each sentence and analyze them.

1) The usefulness of the study of languages is due not only to the frequent political and commercial interests but also to the increasing number of jobs that require a knowledge of at least one foreign language.

This sentence appears to be grammatically correct and does not contain any obvious errors. The structure and word choice seem appropriate.

2) This linguistic enrichment makes a determining contribution to the greatest possibility of cooperation.

This sentence is grammatically correct, but it seems a bit verbose and could be simplified. Instead of saying "the greatest possibility of cooperation," it could be rephrased to say "enhances cooperation to a great extent." This revision would make the sentence more concise and easier to understand.

3) Today, considering the difficulties faced by young people in finding a job at the end of their studies, better possibilities of studying languages would help solve the problem of unemployment, particularly in industrialized countries.

This sentence is well-structured and does not contain any apparent errors. The word choice and phrasing are appropriate for expressing the intended meaning.

Based on this analysis, it seems like all three sentences were written by a native speaker of English. They are grammatically correct and utilize appropriate sentence structures and word choices.