i mean that if you have say a spanish translation, then the home page of your spanish translation will need to have a link to it from your main home page otherwise the spiders will not find your spanish translation

your additional question is a harder one ... there is some talk that hosting several sites with the same host is bad because spiders use the host's ip as part of its spidering but that seems hard to believe in some way as a host may have several customer sites ... so i am not sure about that one

there is talk also of subdomains eg http://english.vacationsbrazil.com are not good but some have reported no problems with that

i would suggest thorough research on the 2 possibilities you have: using subdomains and using separate domains

may be some one in this forum who knows for sure can advise you

serge