Vietnamese vs Chinese
Learn Vietnamese and Chinese at the same time
Vietnamese and Chinese are unrelated (Austroasiatic vs Sino-Tibetan), but centuries of Chinese influence left Vietnamese with a large Sino-Vietnamese vocabulary and similar analytic, tonal structure. Vietnamese is now written in a Latin alphabet.
The short answer
Yes, and Sino-Vietnamese vocabulary makes it rewarding, because many formal words map neatly between the two. Tones are the trap, since similar syllables carry different tone contours. Get one to conversational level first, and learn Vietnamese words with their Hán Việt link in mind.
The verdict
Chinese first makes Sino-Vietnamese vocabulary click; keep the tone systems apart.
Closeness score
8 / 30
Mutually intelligible?
no
Shared vocabulary
Estimates of the Sino-Vietnamese share range widely (often cited around 30% to 60% of the lexicon, higher in formal registers)
Which first?
Chinese first makes Sino-Vietnamese vocabulary click.
Kungfucius says: Vietnamese kept the vocabulary and swapped the characters for diacritics.
Side by side
電話 / 电话
diànhuàSino-Vietnamese reading of 電話; the characters are no longer written in Vietnamese.
大學 / 大学
dàxuéSino-Vietnamese reading of 大學. Note the modifier order matches Chinese here because it is a fixed Sino-Vietnamese compound.
國家 (国家)
guójiāVietnamese keeps the final -c (from Middle Chinese -k) in quốc.