"divisa"
divido, -videre, -visi, -visum   to divide

"partes"
pars, partis f.   part, region

"Gallia est omnis"
Gaul as a whole, all of Gaul

"incolunt"
incolo, -colere, -colui:   to inhabit

"Belgae"
Belgae, Belgarum m. pl.  the Belgians

"aliam"
alius, alia, aliud:  other

"Aquitani"
The Aquitaniens

"qui ipsorum lingua"
who, in the language (ablative) of their own

"appellantur"
appello, appellare:  to call, name

"lingua"
lingua, -ae f. tongue, language

"institutis"
institutum, i n. plan, practice, custom, institution

"legibus"
lex, legis f. law

"differunt"
differro, differre, distuli, dilatus:
to differ, be differengrammar: verbs

"Gallos"
Galli, Gallorum m. the Gauls
[Gallus, -a, -um: of Gaul, Gallic]

"Garumna flumen"
the river Garonne

"Matrona et Sequana"
Matrona, -ae f. : the Marne river
Sequana, -ae f. : the Seine river

"Horum"
of these

"cultu"
cultus, cultûs m. : mode of life, civilization

"humanitate"
humanitas, -atis f. : humanity, refinement, culture

"propterea quod"
propterea: on this account
closely connected with quod: = because

"minimeque"
minime ...saepe very rarely (lit. least often)

"mercatores"
mercator, -oris m.: trader, merchant

"commeant"
commeo, commeare, commeavi, commeatus:
to go back and forth, visit, resort to

"longissime absunt"
absum, abesse, afui:  be distant, be absent
longe abesse:  to be far away

"pertinent"
pertineo, pertinere, pertinui:
pertain to, concern, belong to

"important"
importare:  to import

"proximique"
proximus, -a, um   near

"ea quae"
those things which (is, ea, id)

"ad effeminandos animos"
effeminare: make womanish, weaken, enervate (this term probably no longer politically correct)

"Germanis"
Germani, -orum m. : Germanic people [Germanus, -a, -um: Germanic]

"incolunt"
incolo, incolere, incolui: to inhabit, live, dwell

"continenter"
continually

"trans Rhenum"
across the river Rhine

"bellum gerunt"
bellum gerrere: to wage war

"Helvetii"
the Helvetian, Swiss

"virtute"
virtus, -utis f. courage, bravery

"praecedunt"
praecedo, -cedere, -cesse, -cessurus: to go before; surpass, excel

"fere"
almost

"Qua de causa"
for which reason

"reliquos Gallos"
the rest of the Gauls

"cotidianis"
cotidianus, -a, -um:  daily

"aut"
aut .... aut : either... or

"finibus"
finis, finis m. limit, border; Plural: territory, country, land

"prohibent"
prohibeo, -êre, -hibui, -hibitum:  hold, restrain, keep off, repell

"proeliis cum Germanis contendunt"
proeliis contendere: to contend in battle

"cum"
conjunction:  when

"bellum gerunt"
bellum gerrere: to wage war

"Eorum una pars"
one of their regions (lit. one region of theirs)

"quam Gallos obtinere dictum est"
Acc. cum Inf. construction: "which has been said that the Gauls occupy it", which is claimed to be inhabited by Gauls
obtineo, -tinêre, -tinui, -tentum: hold fast; get possession of; occupy, inhabit 

"initium capit"
initium capere: to tak one's beginning, to start

"continetur"
contineo, -êre, -tinui, -tentum: hold together;
of regions: hem in, bound, border

"attingit"
attingo, -ëre, -tigi, -tactus: touch, reach; 
of territorial divisions: border on, extend to, adjoin

"ab Sequanis et Helvetiis"
= at (lit. from) the side of the Sequanians and Helvetians

"Garumna flumine"
by the river Garonne

"vergit ad "
vergo, vergëre: lie; be situated

"septentriones"
septentriones, -um [septem + trio (plow ox)] the seven stars forming the Big Dipper, hence: the North 

"ab extremis"
ab extremis finibus Galliae: from the remotest region of Gaul

"oriuntur"
orior, oriri, ortum: rise, begin, spring from; start from 
= The (territory of the) Belgian people start(s) at the remotest region of Gaul ...
"pertinent"
pertineo, -ere, -tinui, -tentum:  reach out, extend; pertain to, belong to

"inferiorem"
inferus, -a, um below, lower; Comparative: inferior, -oris: lower

"spectant"
specto, spectare: to look, face (toward)

"in septentrionem et orientem solem"
septentriones, -um [septem + trio (plow ox)] the seven stars forming the big Dipper, hence: the North 
sol oriens: the rising sun, hence East.

"pertinet"
extend

"spectat inter occasum solis et septentriones."
it faces between the setting of the sun and the Big Dipper: = it faces North West