There are some particular problems in the translation process: problems of ambiguity, problems that originate from structural and lexical differences between languages and multiword units like idioms and collocations. Another problem would be the grammar because there are several constructions of grammar poorly understood, in the sense that it isn't clear how they should be represented, or what rules should be used to describe them.

The words that are really hard to translate are frequently the small, common words, whose precise meaning depends heavily on context. Besides, some words are untranslatable when one wishes to remain in the same grammatical category. The question of whether particular words are untranslatable is frequently debated.

For example, it isn't easily to translate a poetry because you need to analyse the words and meaning and after the flow and rhythm (or rhyme). Poetry's most translations are bad. This is principally because the translator knows the foreign language too well and his or her native language too poorly. Some English poetry translations are robotic, do a great disservice to the originals.
Translation Problems:

Problems with the source text:
• Text difficult to read or illegible text
• Spelled incorrectly or printed incorrectly
• Unfinished text
• Badly written text

Language problems:
• Idiom terms and neologisms
• Unsolved acronyms and abbreviations
• Proper name of people, organizations, and places.
• Slang difficult to understand
• Respect to punctuation conventions.

How to teach translation students?
When teaching translation, the first problem for teachers would be the subject. Translation and interpretation are considered together as arts and skills, and teachers must decide from which angle to approach them. If they select art, students will make an infinite series of exercises. If they select skill, students will learn the syntax, accent and terminology.