Isn't this not true? Doesn't Mexican Spanish use different verb tenses than Spain Spanish?

The sounds and spellings of American vs British English are different but nothing so important as conjugations and declensions.

Never thought I would be able to comment here! I’m a native English speaker and an avid learner of Spanish (8 years and a year abroad in Chile). Having lived in and visited several Spanish speaking countries, I can tell you this is completely incorrect. There are several large differences in Spanish dialects throughout Spain and Latin America.

The largest difference between Spain spanish (Castilian spanish) and the spanish spoken in Latin America is vosotros. It is an entire subject (informal you all) used within the language in Spain. Very few other regions use it at all.

There is also a variance in accent depending on the country (or region of the country) the listener is in. Many native speakers can pinpoint another native’s country of origin by listening to a few words of their speech. There’s a difference between Chilean spanish and Argentinian spanish and they share a HUGE border. Some notable difference in accent: Spain uses a th sound for words containing the letters s or c (think of the word gracias said with a bit of a lisp). Argentina uses a sh sound for words with a LL (normally this sounds like a y in English). Besides accent, enunciation and speed play a huge role in distinguishing one speaker from another.

Beyond that, there is slang to consider. Several countries have regional slang making it hard to be completely understood WITHIN their own borders. Other countries simply have nationally known slang that isn’t used anywhere else (I am looking at you, Chile).

All things considered, I would say that Spanish has far more variances from country to country than English does.

Edit: There is even variance in accent and syntax within countries— many have several different regional accents.