If I want to roleplay an interpreter, is there a max number of languages I can learn? Standard human, plan to get 18 INT.
There is no limit, because languages can be learned during downtime
From the SRD section on Downtime Activities, under Training:
You can spend time between adventures learning a new language or training with a set of tools. Your GM might allow additional training options. First, you must find an instructor willing to teach you. The GM determines how long it takes, and whether one or more ability checks are required. The training lasts for 250 days and costs 1 gp per day. After you spend the requisite amount of time and money, you learn the new language or gain proficiency with the new tool.
Given the extensive amount of downtime involved, you may want to know how many languages you can gain from your race, class, and background features. Assuming multiclassing and feats are allowed, a Character that is a:
- Half-Elf (3 languages)
- Acolyte (2 languages)
- Ranger 14 (3 languages)
- Knowledge Cleric 1 (2 languages)
- Mastermind Rogue 3 (3 language)
- Druid 1 (1 language)
- Linguist feat (3 languages)
Xanathar's Guide to Everything
- Prodigy feat (1 language)
should know 18 different languages at level 19.
"Mundane" limits on languages
Using the PHB, it is possible for a human to speak up to 7 languages at character creation without resorting to magical means or class features.
Human: Common, and one extra
Linguist feat (PHB, p. 167): 3 languages
Note that if you pick another race, like half-elf, you can get access to more languages. For example, the half-elf can speak common, elvish, and one extra language. Additionally, the DM can allow you to learn more languages at his/her discretion. It's important to note that your INT score does not affect how many languages you know.
The Cleric's Knowledge Domain grants knowledge of two languages at 1st level (PHB, p. 59). The Ranger gets the language of their favored enemy (PHB p. 91), and the Druid class gets access to druidic, but I'm not sure how useful that is for being an interpreter.
The best class feature for languages is the Monk's Tongue of the Sun and Moon feature, which looks perfect for your interpreter RP (PHB p. 79), though it's a bit high level:
Starting at 13th level, you learn to touch the ki of other minds so that you understand all spoken languages. Moreover, any creature that can understand a language can understand what you say.
The comprehend languages and the tongues spells allow you to understand or read any language, but they don't allow you to speak them. Effects such as telepathy - from the Great Old One Warlock's Awakened Mind feature (PHB, p. 110), for example - bypass the issue of language entirely.
Using magic you can have access to every language. Between Comprehend Languages and Tongues you should be able to speak/understand anything that is thrown at you.
This spell grants the creature you touch the ability to understand any spoken language it hears. Moreover, when the target speaks, any creature that knows at least one language and can hear the target understands what it says.
For the duration, you understand the literal meaning of any spoken language that you hear. You also understand any written language that you see, but you must be touching the surface on which the words are written. It takes about 1 minute to read one page of text.
This spell doesn’t decode secret messages in a text or a glyph, such as an arcane sigil, that isn’t part of a written language.
As far as I'm aware, there is no maximum number of languages in 5e you can learn, but keep in mind they take time and resources to learn (i.e., how would you learn Infernal if you've never encountered it before?). Those spells alone should be more than enough though.
If you are looking at Level 1 in 5e DnD, the most would be 9. Human variant + linguist feat + Sage/Courtier/Anthropologist/etc + Knowledge Cleric. 2+3+2+2 =9, as there are only eight common languages, you can effectively speak with most everyone from the mortal plain.
However, I actually made a build that knows 19 languages by level 11.
Build: Race: Half-Elf (Common, Elvin, and one more) Background: Sage, acolyte, anthropologist, city watch, or courtier (two common languages) Classes -Cleric 1/knowledge: two common languages. -Sorcerer 1/draconic or storm: draconic or primordial, respectively. -Ranger 1: Undercommon from Favored Enemy -Druid 4/Circle of the Shepherd/Prodigy Feat: Druidic, Sylvan, Beast Speech, Halfling -Rogue 4/Mastermind/Linguist Feat: Thieves' cant and all remaining exotic languages.
3+2+2+1+1+3+1+1+2+3=19 languages by level 11.
As you can wild shape into an octopus at Druid 4, you can even read Qualith.
Under the assumption that a character starting at level 11 starts with 5000 + 1d10 x 250 Gold and languages cost 250 gold each to learn, a character starting at level 11 could know all main languages, Druidic and Thieves' Cant (Class Features), and beast speech as well as up to 20 more languages (You should leave spending money for equipment). Thankfully, there are only 18 more non-standard languages (19, if "Minotaur" becomes a new language). Humanoids: Aarakocra, Bullywug, Gith, Gnoll, Grung, Sahuagin, Thri-keen, Troglodyte (8) Non-humanoids: Grell, Hook Horror, Modron, Otyugh, Slaad, Sphinx, Tlincalli, Umber Hulk, Vegepygmy, Yeti (10)
Thus, even with Minotaur, a character starting at level 11 can arguably know all current languages and still have 250+1d10x250 Gold to spend on equipment, plus magical items.
Firbolgs, High Elves, and Yuan-ti Pureblood can match this build as well, just with different skills and stat layouts. Most other races can achieve this with a Belt of Dwarvenkind or spending the last guaranteed 250 Gold and Dwarves can get the same treatment with Demon Armor (Abyssal).
A favorite wild shape would also be Cranium Rat, as they get telepathy, despite only being CR 1/4.
Keep in mind that the Anthropologist background has a feature that helps a character learn humanoid languages much, much faster. Ranger guilds will likely help you find tutors that can teach monstrous languages.
As much as others will argue for Comprehend Languages, Tongues, Eyes of the Rune Keeper, and Tongue of Sun and Moon, spells have time limits and all have other drawbacks.
Eyes of the Rune Keeper: Reads everything, but can't speak everything. Doesn't guarantee writing, either. Comprehend Languages: Can read and hear, but not speak and write. Tongue of Sun and Moon: Talk with everyone, but can't read or write. Tongues: Talk with everyone, maybe read. Not guaranteed to write.
And I guess that's all I can say about ultimate linguist.
This build also allows for assisting the Fighter, Paladin, and Barabian by using the bonus action and reaction to grant advantage on ally attacks from a distance. Throw 4 levels of Bard with the Skilled Feat on, and you have all skill proficiencies with Expertise in half of them.