lorsque nous sommes réunis aujourd'hui
The correct phrase is "today's meeting." Using the possessive form "today's" indicates that the meeting is happening on the specific day that is being referred to.
You don't, it's never a pleasure meeting somebody who's French.
That is the correct spelling of "rendezvous" (meaning a meeting, from French).
The word today is a possessive in the noun phrase "today's meeting" (meeting happening today). The word today is an adverb in the verb phrase "meeting today" (occurring today). The latter is unusual but not unseen in sentences such as "The President will be today meeting with his Cabinet" instead of "The President will be meeting with his Cabinet today" especially if there is a longer object such as "meeting the most vocal critics of his plan to end the ongoing crisis" where the "today" could be too far from the verb modified. More typically, the "today" is used to start the sentence.
They say hello
The translation of "Is there a meeting today?" in French is "Y a t-il une réunion aujourd'hui ?"
plaisir vous rencontrant
La réunion s'est bien passée? (Literally "Did the meeting go well?")
You can say "Comment s'est passée ta journée aujourd'hui ?" in French to ask "How was today?"
You can say "Aujourd'hui, je serai français." in French.
'pour la réunion'
today = aujourd'hui