List of various terms of endearment that can be used in different languages. A lot of them are gender neutral. Now in alphabetical order.
Habibi حبيبي (m) (my love)
Ya hayati يا حياتي (my life)
Ya qalbi يا قلبي (my heart)
Ya ruhi يا روحي (my soul)
Hubbi/hobbi حبي (my love)
Zlato (gold, my precious)
Miláčku (dearest, little dear)
Smukke (pretty/beautiful)
Elskede/elskling (beloved)
Kæreste (dearest and also used for the term girlfriend/boyfriend)
Snut (sorta like babe, a bit outdated)
Smuksak (beautiful but only for endearment)
Pusling (Pus in diminutive)
Musling (mouse diminutive)
Putte[animal] (cuddle[animal of choice], most used is: animal, mouse and pig, but other animals or objects happen)
Allerkæreste (most loved, argumentative)
Basse (cute fat, might come from bear, mostly used for children and men)
Filipino (from various local languages, all gender neutral)
Mahal, sinta (tagalog) (love)
alternatively add "ko" or "aking" to turn it into "my love" (e.g. mahal ko, sinta ko; aking mahal, aking sinta) with "aking" being used more often when talking about the one you love to a 3rd party;
or turn it into a verb (e.g. aking minamahal, kasintahan) to make it "lover"
Paraluman, irog, liyag, giliw (tagalog) (darling) these are older terms though, you won't hear or see them being used unless you're lovers with someone 🌟Extra🌟
Tangi (tagalog) (only one)
Tinatangi (tagalog) (the one i hold dear/the only one for me)
Tinadhana - fated (from the root word "tadhana" meaning fate, which in and of itself should also be a term of endearment and I stand by that)
Hinigugma (bisaya) (beloved) (very old)
Palangga/pangga/langga or "ga" for short and sometimes pagingging (ilonggo) (love) (can also be used platonically or between family members)
Kalasahan (tausug) (beloved) (this is pronounced with an emphasis in the SA syllable (as in kalaSAhan) instead of the LA like in the tagalog word LAsa (which means taste)
Jowa (filipino slang) (significant other/boyfriend/girlfriend)
Bebe, bebe ko, beh, bhe, bhie, bih (filipino slang) (babe)
Lablabs (filipino slang) (literally "love-love" in a heavy filipino accent)
Chéri (m) / Chérie (f) (darling)
Chou (used like "honey", but directly translates to cabbage)
L'/amour de ma vie (love of my life)
Liebling (beloved/favourite)
Schatz (treasure, I would say the most common one between established couples)
Liebes (loved one) (f, I don't find it that romantic)
Liebster (m) (loved one, bit old-fashioned)
Liebste (f) (loved one, bit old-fashioned)
Engel / Engelchen (angel)
Prinzessin (f) (princess)
Kleines (f) (little one, can be used in a cute way for women, but can also sound degrading or offensive)
Αγάπη /Αγάπη μου (love /my love) (the first can also be used among friends, usually between women, but both are very often used in romantic relationships)
Ψυχή μου (my soul) (mostly romantic but can be used by a parent to their kid)
Chaim sheli חיים שלי (my life)
Neshama sheli נשמה שלי (my soul)
Lev sheli לב שלי (my heart)
Meri jaan मेरी जान (f) (my life)
Mera jaan (m/n) (my life)
Sayang (to love/love, can be used as 'honey', doesn't have to be romantic)
Cintaku (my love, mostly used romantically)
Cucciola (puppy/cub) (mostly used for women, but you could say "cucciolo" for men)
Piccola (little one) (mostly for women, "piccolo" would be the male version)
Cara/caro (dear) (now mostly used by grandmas for grandkids but perfect for couples in the past or old couples nowadays
Patata/patatina (potato/little potato) (again mostly women when used romantically, "patato/patatino" for men, but they can also be used for pets, babies, your kids or anyone that you find cute)
Tata/tato (short version of papata/patato)
Polpetta/polpettina (meatball/little meatball) (very uncommon, but I've heard it used for girls)
Topolina (little mouse) (very uncommon, but could be used for girls)
Aegiya 애기야 (baby/little one)
Gongjunim 공주님 (f) (princess)
Wangjanim 왕자님 (m) (prince)
Nae Sarang 내 사랑 (my love)
Yeobo 여보 (darling, loved one to a spouse)
Myszko (f) (little mouse for women romantic, or for young daughters)
Misiu (m) (diminutive bear, romantic for men)
Misiaczku (another form of the above but more intersex)
Słoneczko (diminutive for sun, can be for children but also romantic for women)
Pączusiu (diminutive doughnut, romantic partner)
Bąbelku (bubble diminutive for young children, toddlers or infants)
Duszko moja (very outdated, meaning my soul, for women)
Serce moje (also old school, meaning my heart, unisex)
Gwiazdeczko (diminutive star, for girls and romantic female partner)
Kotek/Kotku (kitten, unisex)
Mała (literally: little (f), for women, can be romantic but also offensive if used by strangers)
Skarbie (my treasure, unisex)
Rybciu (diminutive for fish, little fish, for women)
żabko (diminutive for frog, little frog, for women)
Meu querido (m)/ minha querida (f) (my darling)
Meu docinho (my sweetheart)
Amado (m)/Amada (f) (my love)
Meu (m)/ minha (f) mais que tudo (my above overall) Meu tesouro (my treasure)
Meu bem/ meu benzinho (my goodness)
Meu doce/meu docinho (my sweet/ my little sweet)
Querido (m) / Querida (f) (darling)
Meu bem (untraslatable; something between "my dear" and "my treasure")
Meu docinho de coco (my coconut candy - really old slang, nowadays used only for fun)
Patroa (f) (it means a female boss; not ironic not aggressive, but used by men to describe their wives affectionately, eg. "I can't go today, my patroa is waiting for me at home")
Gato/gatinho (m) / gata/gatinha (f) (cat/little cat; if a person is pretty, they are called a "cat")
Lindinha (beautiful/cutie)
Mozão or Mor (love, more like slang)
Iubi (Sweet heart/darling)
Draga mea (f) / Dragul meu (m) (my dear)
lyubov' moya / любовь моя (my love)
radost' moya / радость моя (joy of mine)
dusha moya / душа моя (my soul)
schast'e moyo / счастье моё (my happiness)
sokrovishche moyo / сокровище моё (my treasure)
solnyshko / солнышко (sunny)
zolotce / золотце (golden)
lyubimyj (m) + lyubimaya (f) / любимый + любимая (beloved)
dorogoj (m) + dorogaya (f) / дорогой + дорогая (darling, dear)
milyj (m) + milaya (f) / милый + милая (dear but in more informal way)
kotik / котик (kitty) malysh / малыш (baby)
zajchik (m) + zajka (f) / зайчик + зайка (bunny)
ptenchik / птенчик (little bird, hatchling)
rybka moya (f) / рыбка моя (my fish)
Miláčik (bit cheesy, but means my lovely)
Kanmani [cun-mun-ee] (darling)
(my husband/my wife, but in a more endearing way, you can say it to a person you're not married yet but thinking about marrying)
Her şeyim (my everything)
Yaşama sebebim (my reason to live)
Ceylanım (My gazelle, it's a gorgeous creature like cmon)
Güzel gözlüm (My lover with beautiful eyes)
Nazlı yarim (My coy lover)
Kalbimin sahibi (the owner of my heart)
Güzelim/yakışıklım (my beautiful/my handsome)
Kediciğim (my kitty/kitten)
Biriciğim/bi'tanem (my one and only)
Balım (my honey) (can also say "bal dudaklım (my lover with honey lips)" if you feeling on fire)
Evimin direği (literally meaning "the post of my house," if you say this to a person (usually your husband), you mean to say that he keeps your household/family up, whether financially or with emotional maturity)
зіронька [zironʹka] (star)
мій світ [miy svit] (my world)
моє життя [moye zhyttya] (my life)
моє серденько [moye serdenʹko] (my heart)
коханий [kokhanyy](m) /кохана [kokhana] (f) (my beloved one)
милий мій [mylyy miy] (m) / мила моя [myla moya] (f) (my dear one)
любий мій [lyubyy miy] (m) / люба моя [lyuba moya] (f) (my loved one)
мій єдиний [miy yedynyy] (m) /моя єдина [moya yedyna] (f) (my only one)
сонце [sontse], сонечко [sonechko] (sun, sunshine)
пташка [ptashka] (f) (birdie)
друг (m)/ подруга (f) моєї душі [druh (m)/podruha (f) moyeyi dushi] (a friend of my soul)
Meri jaan میری جان (my life)
Pyaari پیاری (sweetheart)
Shahzadi شہزادی (f) (princess)
Let me know more terms of endearment in your languages! And please correct me if I'm wrong somewhere.
Please note that they are not all romantic. You can ask in the replies, so a native speaker can answer if it's appropiate for the type of relationship you want your characters to have.
kianamaiart
kaledo-art
theartofmadeline
tangentwithtanner
