In English this sentence begs to be completed. I would swim tomorrow BUT...
Is it the same in Romanian?
Not necessarily. In Romanian, it can also mean "I would like to go swimming tomorrow".
En español, "yo nadaría mañana" suena bien como complemento a alguna otra frase, oración o pregunta, p.e. ¿nadarás hoy?
Neither in Spanish
'I would like to go swimming tomorrow' seems better.