1. Caesar 1.2-3

2. Apud Helvetios longe nobilissimus fuit et ditissimus
Orgetorix. Is M.Messala, [et P.] M. Pisone consulibus 
regni cupiditate inductus coniurationem nobilitatis 
fecit et civitati persuasit ut de finibus suis cum
omnibus copiis exirent: perfacile esse, cum virtute 
omnibus praestarent, totius Galliae imperio potiri.
Among the Helvetii Orgetorix was by far the most noble and the wealthiest. He, (when) M. Messala and P. M. Piso (were) consuls, was influenced by a desire for nobility to make a conspiracy and to persuade the state to go out from their own territories with all their troops: (he thought it) to be very easy, since they surpassed all (others) in courage, to gain control of the empire of the whole of Gaul.

3. Id hoc facilius iis persuasit,quod undique loci natura
Helvetii continentur: una ex parte flumine Rheno 
latissimo atque altissimo, qui agrum Helvetium a 
Germanis dividit; altera ex parte monte Iura altissimo,
qui est inter Sequanos et Helvetios;
He persuaded them by this that it (would be) rather easy, because on all sides by the nature of the location the Helvetii were contained: from one part by the very wide and very deep Rhine river, which divides the field of the Helvetii from the Germans; from the other part by the very tall mount Jura, which is between the Sequani and Helvetii.

4. tertia lacu Lemanno et flumine Rhodano, qui
provinciam nostram ab Helvetiis dividit. His rebus 
fiebat ut et minus late vagarentur et minus facile
finitimis bellum inferre possent; qua ex parte 
homines bellandi cupidi magno dolore adficiebantur.
On the third (side) by lake Lemannus and by the Rhone river, which divides our province from the Helvetii. By means of these things it happened that they were roaming around less broadly and they were able to inflict war on the neighboring peoples less easily; from which part the people eager for waging war were annoyed greatly.

5. Pro multitudine autem hominum et pro gloria belli
atque fortitudinis angustos se fines habere 
arbitrabantur, qui in longitudinem milia passuum 
CCXL, in latitudinem CLXXX patebant.
However in consideration of the multitude of people and in consideration of the glory of war and bravery they were judging themselves to have narrow boundaries, which lie in length 240 and in breadth 180 (Roman) miles.

6. [3] His rebus adducti et auctoritate Orgetorigis permoti constituerunt ea quae ad proficiscendum pertinerent comparare, iumentorum et carrorum quam maximum numerum coemere, sementes quam maximas facere, ut in itinere copia frumenti suppeteret, cum proximis civitatibus pacem et amicitiam confirmare.
Having been influenced by these things and having been moved by Orgetorix’s authority, they decided to prepare the things which pertained to setting out; to buy as great a number of yokes and carts as possible, to make as great a sowing as possible, in order that a supply of grain be supplied on the journey, to strengthen the peace and friendship with the nearest states.

7. Ad eas res conficiendas biennium sibi satis esse duxerunt; in tertium annum profectionem lege confirmant. Ad eas res conficiendas Orgetorix deligitur. Is sibi legationem ad civitates suscipit.
For finishing these things they judged two years to be enough for themselves; in the third year they declared their departure with a law. For completing these things Orgetorix was chosen. He undertook/took up for himself an embassy to the states.
NOTE: confirmant AND deligitur AND suscipit are PRESENT tense verbs, but it sounds weird in English to keep them in the present tense. We call this tense the “historical present” and it is FINE to translate them as past tense AS LONG AS YOU ARE CONSISTENT.

8. In eo itinere persuadet Castico, Catamantaloedis filio, Sequano, cuius pater regnum in Sequanis multos annos obtinuerat et a senatu populi Romani amicus appellatus erat, ut regnum in civitate sua occuparet, quod pater ante habuerit;
On this journey, he persuaded Casticus, son of Catamantaloedus, a Sequanian, whose father had held absolute authority/political power in/over the Sequani for many years (note the accusative of duration of time) and had been named a friend by the Senate of the Roman People (or a friend of the roman people by the senate), to seize absolute/political power in his own state, which his father had held before;

9. itemque Dumnorigi Aeduo, fratri Diviciaci, qui eo tempore principatum in civitate obtinebat ac maxime plebi acceptus erat, ut idem conaretur persuadet eique filiam suam in matrimonium dat.
and in like manner Dumnorix the Aedui, the brother of Diviacus, who at that time was holding chief authority in (his) state and had been accepted greatly by the common people, he persuaded to try/attempt the same thing and he gave his own daughter to him in marriage.

10. Perfacile factu esse illis probat conata perficere, propterea quod ipse suae civitatis imperium obtenturus esset: non esse dubium quin totius Galliae plurimum Helvetii possent; se suis copiis suoque exercitu illis regna conciliaturum confirmat.
He demonstrated to those people (that) it was very easy to do the things having been attempted to accomplish (i.e. that it was easy to do the things they attempted to accomplish), because he himself was going to possess absolute authority of his own state: there was no doubt that of the whole of Gaul the Helvetii could most (i.e. they were the most powerful); (and) he established/affirmed that he was going to secure with his own forces and with his army sovereign powers (literally kingdoms) for those men.

11. Hac oratione adducti inter se fidem et ius iurandum dant et regno occupato per tres potentissimos ac firmissimos populos totius Galliae sese potiri posse sperant.
Having been influenced by this speech, they gave a pledge and an oath among themselves and, political power having been obtained, they hoped that through three very powerful and very strong peoples they could take possession of the whole of Gaul.