OK, so the artificer is the most complicated class in the game and you probably don’t want to play it. The wizard is definitely complicated, and with the right tack can do the things you’re interested in, but it’s possibly overpowered plus doesn’t really seem to have the imagery you want out of the box.
Enter the Beguiler
The beguiler from Player’s Handbook II is not as complicated as the wizard. Rather than maintaining an ever-expanding spellbook and preparing spells every morning, the beguiler just knows every spell on his spell list, and can use them in any combination he likes provided he’s still got spell slots left for the day. And ultimately, the beguiler’s not nearly as powerful.
On the other hand, the beguiler is far more obviously stealth-oriented. They have Hide and Move Silently as class skills, they can wear light armor, and they get bonuses for surprising people with their spells. Their spell list is quite good, with lots of different options, including an incredibly flexible array of illusions.1 Their 6+Int skills mean they are quite likely to have solid mundane skills for sneaking about and slipping into places they shouldn’t be.
I recommend considering the Master of Poisons and Poison Spell feats (both from Drow of the Underdark) to excel with poisons. I recommend against actually playing a drow, though, master poisoners though they are, because the LA +2 is very, very bad.
Also, the mindbender prestige class from Complete Arcane, though generally quite poor, is an amazing choice for a beguiler to take for a single level at 6th (i.e. 5th-level beguiler/1st-level mindbender). The entry is easy, and mindbender improves your spellcasting while giving you telepathy out to 100 ft., which qualifies you for the excellent Mindsight feat (Lords of Madness). Now you know exactly where every thinking mind in 100 ft. is, and that’s awesome. Continue taking beguiler levels thereafter (i.e. 5th-level beguiler/1st-level mindbender/beguiler +x)
- Just how flexible and useful illusions are does depend a fair bit on the DM, so you should ask about that before making a character focused on them, but in my experience most DMs are willing to let them go pretty far.
Double Jeopardy
OK, so maybe the beguiler sounds pretty cool and all, but you actually liked the way that wizard was sounding. No problem: the ultimate magus prestige class from Complete Mage is an excellent option, and nothing works so well for it as the beguiler does. Start out as a 1st-level beguiler for the sweet, sweet 4×(6+Int) skill points, and then multiclass into wizard for three levels in order to qualify for ultimate magus. Ultimate magus will improve both beguiler and wizard spellcasting. Make sure to take Practiced Spellcaster (beguiler) before you start; Practiced Spellcaster is also from Complete Mage. Being an illumian and taking the Power Sigil (Krau) feat, both from Races of Destiny, is also highly recommended.
In this approach, being a specialist wizard banning Enchantment and Illusion is a good idea because beguiler is very strong in both of those schools, so you won’t miss those spells as much. Conjuration or Transmutation are probably your best bets for specialty, though really anything can work. Practiced Spellcaster (beguiler) is a must and Power Sigil (Krau) is highly recommended, but aside from that you can still take Master of Poisons and Poison Spell. If you are a human subrace—and illumians are—, also consider Able Learner to allow you to more easily maintain your ranks in Hide and Move Silently.
Sylvan covers plant creatures and lots of other 'forest' creatures other than fey, it's a pretty good choice for what you're going for.
Terran on the other hand, is a bit rarer. Very little speaks Terran. In my games, I have underground creatures often speak Terran, aerial/flying creatures often speak Auran, underwater creatures often speak Aquan, and a disproportionate number of outsiders speak Ignan.
But RAW, you're looking at like, Earth Elementals, most of which don't talk to people. Summoned Creatures charge at foes automatically, so you don't need to talk to them usually.
Language choices - Treant is a language in pathfinder, or as I like to call it, Entish. That would work for a druid. Unlikely to come up though.
You already speak Common and Elven, but Dwarven is the other traditional trifecta of languages, although nearly all GMs will never have it be important.
Undercommon covers probably the broadest category of races and situations, but again most GMs won't have it come up.
Surprisingly large numbers of common PC enemies speak Giant, and ogres, giants etc are all 'wild' humanoids, they mostly don't live in cities.
Dragons and dragon-related things are pretty common, and Draconic is also (apparently) the most common language of arcane magic (sort of like Latin in Ars Magica).
Just have a look here, and pick something interesting. Mention to your DM that a big part of your character is that your character considers himself a linguist, and the DM might get ideas about working that into the story.
Best Answer
I would recommend starting with a race that provides a Wis bonus and a bonus to Con or Dex, so Elf, Dwarf, Razorclaw Shifters, Githzerai and Wilden of the various PHB races.
Using an array of 15, 15, 15, 11, 10, 8 for stats you can get Wis and either Con or Dex to 17, and then Str and the other get 15 and 11, giving you a pretty beefy 17, 15, 11 in your physical ability scores, and still retaining a 17 Wis.
Unfortunately Driuds lack at-will powers with secondary stat kickers, so your secondary stats being high isn't as much of a win as it is for many other classes.
The starting -2 to hit that you suffer against the pre-racial adjusted 18 wisdom druid can be mitigated first by taking implement/versatile expertise, superior implement training-accurate staff, and also your odd number in wisdom means that a level 4 attribute boost to wisdom gives you a +1 to hit.