Contrarily to European languages, Japanese has many different pronouns for each person (I, you, he/she, we...). "I" and "you" have an especially wide range of translation with various nuances, politeness level and gender. Learning is particularily useful to read mangas. I know the following ones (I am sure there are more, among old fashioned ones).

I" and "We"

• Watakushi 私 : Most polite and formal version
• Watashi 私 : most common. Used more by women than men.
• Atashi あたし : Mostly used by young females. Sounds cute.
• Atai 私 : Slang version of "Atashi"
• Washi わし : Mostly used by older men to younger or lower rank people.
• Uchi うち : Used mostly by women. A neutral version also refers to "us" (family, company, etc.) as opposed to "them" or "you".
• Jibun 自分 : Neutral. Refers to the "self", so can be use for "I" or "you". "Jibun no" (自分の) means "my" or "your" and "jibun de" (自分で) means "myself" or "youself".
• Boku 僕 : Common for younger men (sometimes women). Sounds more refine than "ore".
• Ore 俺 (also "Ora" in dialect) : Used by virile or older men. Not as polite as "watashi".
• Oresama 俺様 : Arrogant and rude version of "Ore"
• Orera 俺ら (also "Oira" in dialect) : Plural of "Ore"
• Onore 己 : Used by men. Sounds arrogant and impolite. Also means "self" or "you" (see "Jibun").
• Sessha 拙者 : Used by men (formerly samurai). Humble and polite.
• Ware 我 : Quite formal and polite, but old-fashioned (except plural "wareware", used in a humble way to talk about one's company).
• Wa(ga) 我（が） : Literary for "watashi". Still used in the meaning of "my" or "our" (eg : "Wagakuni" わが国 = my/our country).
• Kochitomo こちとも : Slang for "we" or "ourselves", sometimes also "I" and "myself".
• Wate わて : Kansai dialect for "Watashi".
• Chin 朕 : Used by emperors or kings.
• Daikou 乃公 : Literary. Used by men when speaking in an haughty way.
• Soregasi 某 : Ancient form of "Watakushi".
• Warawa 妾 : Ancient form of "Watakushi".

"You"

• Anata 貴方/貴女 : Most usual and polite form.
• Anta あんた : Informal version of "anata".
• Kimi 君 : Used by men to talk to younger women or children, or to intimate people.
• Omae お前 : Used by older or less refined people. Less polite than "anata" and sometimes almost rude.
• Temee 手前 : A bit rude and aggressive.
• Kisama 貴様 : Usually rude and including bad feelings.
• Jibun 自分 : Neutral. Refers to the "self", so can be use for "I" or "you". "Jibun no" (自分の) means "my" or "your" and "jibun de" (自分で) means "myself" or "youself".
• Onore 己 : Used in a disdainful way.
• Onushi (onoshi) 御主 : Polite and humble. Used by samurai to talk to people of equal or lower rank. Literally means "master".
• Nanji (namuchi, nare) 汝 : Literary. Used with intimate people or lower rank people.
• Onmi 御身 : Literary honorific form meaning "your body".
• Sochi そち, Sokotomo そのとも, Sonohou その方, Sonota そのた, Konota このた : dated variant of "Anata", all meaning something like "hey there ! They are informal and impersonal."

"He/she/they"

• Kare/kanojo 彼/彼女 : Most usual and neutral form of "he/she"
• Koitsu, soitsu, aitsu こいつ、そいつ、あいつ : means "this/that guy"
• Yatsu 奴 : rude, involve bad feelings

Just add "ra" after any of them to form the plural.

The plural can be form by adding the suffix "-ra" (for pronouns that end in -e or -u) or "-tachi" (for those that end in -i and -a). For example : watashitachi, anatatachi, temeira, karera, aitsura... One exception is "ware", which plural is made by doubling the word ("wareware").