English-Vietnamese Dictionaries are both helpful and not so helpful.
Words for physical objects
Words such as car, train, bed, house, cup, sugar, etc. have correct translations because of the obvious physical image behind the word.
Words expressing concepts, ideas, feeling and thought
Dictionary translation of many words such as envy, jealous, dear, feel comparison for (thương), frustrate, etc. can be rough or different from intended meaning. One word that appears in almost any official correspondence is ‘dear’ which should be translated as ‘kính gửi’. Yet, this simple translation is even not listed in many dictionaries. Another word frequently encountered in conversations in Vietnamese culture is ‘thương’ (feel comparison for), which is translated differently as ‘love’ by most dictionaries.
In law, translation of ‘thương’ as ‘love’ would incriminate a unrelated party. In 2009, at a trial in the UK, a defendant rejected a court interpreter as he was unimpressed with the interpreter translating ‘thương’ (feel comparison for) as ‘love’. Needless to say, in good or bad time, most of us would be more likely to confide in someone we love, instead of someone we feel comparison for.
The key difference in monolingual and bilingual dictionaries is the native language. As no one can really have two native languages, either the understanding of the source language or the translating into the target language will not be at the native level. For most Vietnamese dictionaries the editors are likely native Vietnamese so the interpretation of English is sometimes 'foreign' in relation to the conceptual meaning of the word, its connotation or how it is used.