I’ve tried to base the available languages on the closest that are available through the proper channels, so you can just click on the equivalents in Character Builder. Consequently, I’ve mapped the most obscure (in this land) to Abyssal and Supernal.
Abyssal (Mekhem): Burning Sands humans
Chondathan (High Rokugani): Rokugani humans (court)
Common (Rokugani): Rokugani humans
Damaran (Yaban-jin): Yaban-jin humans
Deep Speech (Mujina): Trickster spirits
Draconic (Kenku): Kenku
Dwarven (Nezumi): Ratlings
Elven (Chikushō-do): Animal spirits
Giant (Oni): Shadowlands, Tainted
Goblin (Bake-Mono): Goblins
Language of the mind (Naga): Naga
Primordial (Kami): Elemental spirits, gods, and Fortunes
Shou (Moto): Rokugani humans (Unicorn Moto/Ujik-hai)
Supernal (Senpet): Senpet humans
Thayan (Ashalan): Ashalan
Untheric (Ivory Kingdoms): Ivory Kingdom humans
Other than characteristics related to their undead and construct keywords, creatures can be studied by different knowledge skills based on their origins, so you’ll want to know what I’ve decided on those.
Aberrant (Dungeoneering): Trickster spirits (Sakkaku)
Elemental (Arcana): Elemental spirits and Fortunes (Tengoku)
Fey (Arcana): Animal spirits (Chikushō-do)
Immortal (Religion): Spirits of the dead (Gaki-do, Tōshigoku, Yomi, Yume-do)
Natural (Nature): Mortals such as real animals, humans, and ratlings (Ningen-do)
Shadow (Arcana): Tainted creatures such as oni and goblins (Jigoku and the Shadowlands)
Shields are not known in Rokugan. If you want to use a parrying fan (tessen), I suggest you take an off-hand bludgeon and the Two-Weapon Defense feat. Interestingly, without divine classes and shields, there are none who wear plate armor, which is appropriate to the level of brutish tin-can-ness they have in this setting. I have picked rough equivalents to fit the culture (and the fact that none but the most iconoclastic samurai would be wearing dead animal parts), but you can call it what you wish; the main thing is a matter of how heavy it is.
Scale: Splint (partial armor to ō-yoroi)
Other than a lack of crossbows, you can find most any simple or military weapon, regardless of what you want to call a particular size of axe, hammer, or spear. The main question is about the samurai’s iconic twin swords, which I’ve handled differently from the 3rd-Edition standard.
Uchi-Gatana: The main arming sword that is most commonly meant by the word “katana,” the sword that can be used one-handed but more commonly two-handed is represented by curved heavy blades in my setting. I feel that the high crit property better shows the difference between these slicing weapons and the straight chopping blades more commonly used for their weight by other cultures. It also works well with the quintessential samurai character theme, which would represent the best quick-draw experts of the Kakita school of the Crane. I was sadly completely wrong about being able to use a scimitar properly two-handed, as it was not given the versatile property in 4th Edition. So, usually one will be used in two hands for precision, counting as a falchion, while those who dual-wield will prefer to count it as a scimitar. There could also be unusual rapier-like blades for those who want them for other reasons.
Waki-Zashi: The secondary sword of a warrior can be represented by a short sword. However, the one carried by non-bushi samurai, such as shugenja and non-combatant courtiers, would better be equivalent to a sickle, since they would not likely be spending feats on mêlée weapon proficiencies.