In poetry one is allowed to ignore grammar; you may add and subtract syllables to make the rhythm work or make up words if English does not have one you like.
If you have done this deliberately then ignore the following but if it is unfamiliarity with English rules then I hope this helps. (and I am really impressed by the thought of writing poetry in a foreign language.)


Time to say goodbye,
smiling, or weeping,
slowly you pass me by,
remember the first time we meet, (this reads as an order for a first meeting in the future. "we met" would be past tense)
in that time, some of you are raucous, some of you shy (present tense is often used in English to add power to a description of a past event)


Time to say goodbye,
in the air, your singing seems still lingering there,
do you know, your laughters are the best songs, (laughter like water is seldom pluralized unless you do it to emphasize that each individual's laughter has their own separate song. Possibly "your laughter makes the best songs" or "made" for past tense)
'cause it comes from a pure voice and heart,
and no bad guy dares to look into your eyes, and no one can tell you a lie.



Time to say goodbye,
But no cry (only if the speaker is Jamaican otherwise "don't cry")
Do you know everybody parted will meet again,
we come from the same universe,
Have a big rejoice, blossoming and prosperous, be deadly happy, (rejoice is a verb and I am not sure what to suggest. Maybe "a big rejoicing"?) (deadly happy is not a common English phrase and feels very dark, implying that the happiness could kill you. It doesn't seem to fit with the rest of the verse.
before we reunite, returning everything when we die


Please ignore anything that is not helpful.

PS I read "tell it slant" as don't be too straightforward; come at the truth from an angle so that it doesn't hit too quickly.