yoshi よし

In Japanese, yoshi よし means "alright!" It's often an expressions used when you're ready to do something—"alright, let's go!"—or it can simply mean something is okay—"that's alright too."

Sometimes, it's pronounced yooshi よーし instead.

Manga: One Piece, Wan Piisu ワンピース (Chapter 598)

Usage

The word yoshi よし has two different, separate uses.

In the first one, it means "good," "alright." This is related to the adjectives ii いい, yoi よい, which also mean "good," to the point that yoshi, ii, and yoi are in some cases interchangeable.

kore ga ii これがいい
kore ga yoi これがよい
kore ga yoshi これがよし
This is good.

Note that yoshi may also be spelled yoshi 良し, with the same kanji as ii 良い and yoi 良い.

Grammatically, yoshi 良し is a ku-adjective, which were more common in old Japanese. Basically, yoshi means "good" but it's not used in that sense in modern Japanese. Instead, yoi, or rather, ii, would be the word you use to mean "good."

However, characters that speak anachronistically may use yoshi instead of ii to mean "good."

The other use of yoshi よし is an expression to mean "alright." This is used before you decide something, sometimes enthusiastically. Could be when you decide something by yourself, or when someone else does something and you go "we're all set, let's do this."

yoshi, sore de ii
よしそれでいい
Alright, that's good. (let's keep it that way.)
yoshi, ore mo yaru
よし、俺もやる
Alright, [I'll] do [it] too.

This expression is very common in modern Japanese, so most of the time yoshi means "alright" rather than mean "good."

For example, yoshi is often used before going to do something:

よし　いくか！！ quote from manga One Piece ワンピース (Chapter 598)

Manga: One Piece, Wan Piisu ワンピース (Chapter 598)

yoshi, iku ka!!
よし　いくか！！
Alright, [time to] go!!
- This is the verb "to go," iku 行く, with the question particle ka か. It doesn't make much sense in English. To understand this, let's see another phrase:
- ikou ka 行こうか
  Let's go? (I'm inviting you to go, come on already.)
- The phrase iku ka is the same invitation but toward himself, in the sense of "I should go now?" Or "do I want to go now?"

Manga: School Rumble (Chapter 1)

Context: first page of a manga.
pikon ぴこん
*hair springing* (mimetic word.)
koukou ni-nensei ka...
高校２年生か･･･
Second year high school student, [huh]?
yoshi!
よし！
Alright!
saaa
さーー
[Come!] (in the sense of being ready for it.)
kyou kara shin-gakki da!
今日から新学期だ！
From today on [it's] a new school term!
ganbaru zo!!
頑張るぞ！！
[I'll] work hard!!

Kore de Yoshi これでよし

The phrase kore de yoshi これでよし means "with this it's alright" or "by this it's alright." It's often used after a characters fixes or patches up something, or equips some equipment, etc. Implying it wasn't alright before, but "with this" done, it's alright.

To have a better idea of how kore de works:

yoshi, kore de owari
よし、これで終わり
Alright, with this [it's] the end.
- Alright, with this [I'm finished doing this stuff].
- Alright, with this [I'm done].
- (used when you finish a task or when you're done with a job, for example.)

In this case yoshi is almost synonymous with ii いい. This happens because a verb in te-form plus ii (te-ii) can mean "this is alright." In kore de ii これでいい, the de で is the te-form of the copulative verb da だ.

However, there are differences between kore de ii and kore de yoshi.

For starters, te-ii may sound like you're for permission to do things, or questioning whether something is alright, while te-yoshi is always affirmative

kore de ii これでいい
This is alright.
kore de ii? これでいい？
Is this alright?
kore de yoshi! これでよし！
This is alright!

tabete ii 食べていい
[You] can eat it.
tabete ii? 食べていい？
Can [I] eat it?
tabete yoshi 食べてよし
[You] can eat it. It's alright to eat it.

Another thing is ii has other arcane meanings. It can even mean "unnecessary" sometimes because when you're "alright" you "don't need" help. The word yoshi doesn't have such meaning.

Sore mo Yoshi それもよし

The phrase sore mo yoshi それもよし means "that's also alright."

The phrase sore mo ii それもいい is similar in that it means "that's also good." One difference is that sore mo ii can mean "that's also unnecessary" depending on context, while sore mo yoshi always means "alright."

Yoshi to Suru よしとする

The phrase yoshi to suru よしとする means "to say that's good enough." More literally, it means "do as [it] were good." It's used when you do something and maybe there's more you can do, maybe not, but anyway, let's say it's enough as it is and our job here is done.

yoshi to shiyou よしとしよう
Let's say it's good enough. (this is the volitional form, used to invite someone to say it's enough.)
ysohi to shita よしとした
I decided that was good enough.
I acted as if that were good enough.
I went on as if that were good enough.
(this is the past form.)

Yoshi in Japanese

Yoshi in Japanese is Yosshii ヨッシー. I mean, the Yoshi from Super Mario Bros. is called Yosshii ヨッシー in Japanese. Do what you will with this information.

Game: Super Mario World

fuu' フーッ！
Fuuh.
tasukatta. 助かった。
[You] saved [me].
boku Yosshii
僕ヨッシー
I [am] Yoshi.
Kuppa ni tsukamatta nakama wo tasuke ni
oshiro e ikou to shitara
クッパにつかまった　なかまをたすけに　おしろへいこうとしたら
[When I] went to save my friends [that were] captured by Bowser. (Bowser's Japanese name is Kuppa, see: Bowsette / Kuppa-Hime.)
yatsura ni tamago ni tojikomerareta-n-desu.
やつらに　たまごに　とじこめられたんです。
[I] was sealed inside an egg.
- tojikomu 閉じ込む
  To put in and close. (i.e. he was put into the egg, and then the egg was closed, sealed, trapped.)
Wait, what?
Seriously?
The Yoshi aren't born out of the eggs with shoes and saddles when you find them, they're adult Yoshi sealed inside eggs with magic or something?
I can't believe this.