Prepare to die.

[Alessio]

Please allow me to correct the Italian translation.

Italian
Salve. Mi chiamo Inigo Montoya. Tu hai ucciso mio padre. Preparati a morire.
/'salve mi 'kjaːmo i'niːgo mon'tɔːja tu ai ut'tʃiːzo mio̯ 'padre pre'parati a mo'riːre/
hello 1SG.REFL call.1SG Inigo Montoya 2SG kill.PAST.2SG my.M father prepare.IMP+2SG.REFL to die

I will include an explanation.
"Piacere" would be okay in place of "salve", but since it means "nice to meet you", I just find it a bit unnatural when said to someone you're about to kill. So I went for a more formal version of "hello".
"Il mio nome è" is also unnatural, although correct and sometimes used in badly translated movies. The "normal" way to say this in Italian is "mi chiamo".
"Uccideva mio padre" is plain wrong, because it's a continuous tense and it just makes no sense whatsoever here. I went for "Tu hai ucciso mio padre", dropping the formality of the 3sg - since you're about to kill someone, it would be, once more, unnatural - and adding an explicit subject, which slightly emphasizes the fact that the listener is, in fact, the killer.
"Preparati a morire" is just the 2sg (informal) version of "Si prepari a morire".

Here's a translation in my regional language as well:
Emilian - Dialàt Vgnulěṡ
Sciâvo. A-m ciâm Inîgo Montôya. Tè t'ě quàl ch'l'à mazê mě pêder. Parpêr-et a murîr.
/'stʃaːvo am tʃaːm i'niːgo mon'tɔːja tε te(ː) kwɐl kla mɐ's̪εː meː pεːder pɐr'pεːret a mʊ'riːr/
hello 1SG.REFL call.1SG Inigo Montoya 2SG.TON be.2SG the_one who+kill.3SG.PAST my father prepare.IMP+2SG.REFL to die

[Threr]

Bonjour. Je m'appelle Inigo Montoya. Vous avez tué mon père. Préparez-vous à mourir.

Deyryck

Kat'da Nakô inigo'montoya da Bêb tkénopa' Lig' kové
hello.GOAL:none name: inigo montoya GOAL:none dad you.kill.PAST.GOAL:none death prepare.INJ

[Iyionaku]

शोड़ं. नौ शूनुं शोज़ शिनिगु मॢतूय. यो तिऌपेज़ मूदू नेये पीतेर. षुषुमेज़ काफेमे.
Ēram. Ney ūnum ēs Inigu Muntūya. Yē tilpes mūdū neye pīter. Șușumes kāpheme.
Hello | 1SG.POSS.MASC.NOM name.NOM COP.3SG.MASC PROP | 2SG.MASC.NOM AUX.AOR.2SG kill.PP 1SG.POSS.MASC.ACC father.ACC | prepare.IMP.2SG die_forcefully.INF
Hello. My name is Inigo Montoya. You killed my father. Prepare to die.

[Iyionaku]

Caelian

Wandësëm. Rar Inigui Montoya bipustal. Zan bonnuip Rabyeng sikilkim. Bye fonrapic.
[wandəˈʒəm | rah iniˈgʊɪ̯ mɔntɔˈja bipʰuʃˈtʰal | zan bɔnʊɪ̯p raˈbʲɛŋ ʒikʰilˈkʰim | bʲɛ βɔnraˈpʰiç]
pretty.VOC | 1SG.NOM Inigo.ACC Montoya STAT-call.1SG | 2SG.NOM father.ACC 1SG.GEN-ACC PST-kill.2SG>3SG | COP.2SG>3SG life.TERM
Hello. My name is Inigo Montoya. You killed my father. Prepare to die.

I didn't have a word for "to prepare" and was to lazy to create one, so I instead paraphrased it as "Be the end of life"

[Znex]

Yorkish
Heʒ. Ʒ'am Inigo Montoʒa. Tha fellt me father. Bou thasʒen at deʒ.
/hei | jam 'ɪnɪkʊə mɒn'tɒjə | θa fεlt mə 'faθər | puː θə'ɕɛn ə tei/
INTJ | 1SG=be.PRS.1SG Inigo_Montoya | 2SG kill-PST 1SG.POSS father | make_bound 2SG-REFL INF die
Hello. I'm Inigo Montoya. You killed my father. Prepare yourself to die.

[lsd]

3SDL:
lÀÞºUÖnU³±mÀU³±TlÀ
(my father past killed by you now killed by me...)

[Batz]

Naguil

Mindei dimian. Eldalmanas Inigo Montoia. Ailyrnil elvoruin. Guves ailirnien.
/'mindɛ.i 'diːmi.an | ɛl'dalmanas i'niːgɔ mɔn'tʰɔːia | aɪ̯'lyːrnil ɛl'vɔːru.in | 'guːvɛs aɪ̯’liːrni.ɛn/
Mind-ei dim-ian. El-dalm-an-as Inigo Montoia. Ai-lyrn-il el-vor-uin. Guv-es ai-lirn-ien.
day-ACC good-ADJ.ACC. 1SG-name-PRS-MED Inigo Montoya. 2SG-kill-PST 1SG-father-ACC. Prepare-IMP.MED 2SG-death-ALL.
Good day. I name myself Inigo Montoya. You killed my father. Prepare yourself for your death.

[Flavia]

Abaniscen

alhasi. ni Inico Montoia niestel. bi matumale i ni chiusce ayana. chiusce turasih.
greet-SUBJ | 1s.O Inigo Monotya name | 2s.O father.O 3s.O 1s.O dead cause | dead prepare<SUBJ>
[ʔáːɬaɕi | ɲijĩ́ɲikɔ̃mṍːntɔja ɲéːstɛl | bʲỹmɑ́ːtũmɑléːjĩni çuskɛʔáːjãna | çuskɛtúːɾas(ĭ̥h)]
Greetings. I am named Inigo Montoya. You killed my father. Prepare to die.

Translation challenge 11%

[lsd]

I post it elsewhere...

[Arayaz]

Ngama

Masyè. Leʔ cènya weʔIniko Mámtóya mahóm. So khè thó ma. Soniʔ mò ma khè so.
masyè / leʔ cè-nya weʔ-ʔiniko mámtóya ma=hóm / so khè thó ma / so-niʔ mò ma khè so
1-hope / 3pl.HUM give-name APP=Inigo Montoya 1=DAT / 2 kill father 1 / 2-should prepare.for 1 kill 2
[məʃɛː] / [leʔ tsɛːɲə weiniɡo maːmtoːjə məhoːm] / [so kʰɛː tʰoː mə] / [soniʔ mɔː mə kʰɛː so]
Hello. My name is Inigo Montoya. You killed my father. Prepare for me to kill you.

TC: 34%

[Flavia]

Early stage of unnamedminimalphonologybaltoslaviclang

Palan. Jás em Inigo Montoya. Tú úbíl esi maj atik. Katawáti ná míl.
[pəɫən | jɑːzɛm [...] | tuː ʔuːbɪlɛsɪ məj ətɪk | kətəwɑːtɪ nə miːl] (?)
hello / 1sg be.1s I. M. / 2sg kill-PTCP AUX-2sg my father / prepare.IMP for death

Spoiler:

Words:
*palan − cognate of PSl *poklonъ, from *pa + *klanītei?, to bow down;
*atik − cognate of PSl *otь̀cь, from *atiku(s);
*katawáti − cognate of PSl *gotovati, possibly a Gothic borrowing (?);
*míl − from PBSl *mirtís whence PSl *sъ-mьrtь;
*úbíl esi − a periphrastic construction like the one in Old Polish, possibly an influence for the latter (attested very early), it displaced the other past tenses because their forms became hard to distinguish after the loss of /x/.