Most of the localization options are for title tooltips over icons.

You can provide localization options to override the tooltips as well as the day/month display.

You could also set this globally via tempusDominus.DefaultOptions.localization = { ... } or by creating a variable e.g. const ru = { today:'Перейти сегодня' ... }; then provide the options as

new tempusDominus.TempusDominus(document.getElementById('datetimepicker1'), {
   localization: ru
 }
     

new tempusDominus.TempusDominus(document.getElementById('datetimepicker1'),
  {
    localization: {
      today: 'Go to today',
      clear: 'Clear selection',
      close: 'Close the picker',
      selectMonth: 'Select Month',
      previousMonth: 'Previous Month',
      nextMonth: 'Next Month',
      selectYear: 'Select Year',
      previousYear: 'Previous Year',
      nextYear: 'Next Year',
      selectDecade: 'Select Decade',
      previousDecade: 'Previous Decade',
      nextDecade: 'Next Decade',
      previousCentury: 'Previous Century',
      nextCentury: 'Next Century',
      pickHour: 'Pick Hour',
      incrementHour: 'Increment Hour',
      decrementHour: 'Decrement Hour',
      pickMinute: 'Pick Minute',
      incrementMinute: 'Increment Minute',
      decrementMinute: 'Decrement Minute',
      pickSecond: 'Pick Second',
      incrementSecond: 'Increment Second',
      decrementSecond: 'Decrement Second',
      toggleMeridiem: 'Toggle Meridiem',
      selectTime: 'Select Time',
      selectDate: 'Select Date',
      dayViewHeaderFormat: { month: 'long', year: '2-digit' },
      locale: 'default',
      startOfTheWeek: 0,
      /**
       * This is only used with the customDateFormat plugin
       */
      dateFormats: {
        LTS: 'h:mm:ss T',
        LT: 'h:mm T',
        L: 'MM/dd/yyyy',
        LL: 'MMMM d, yyyy',
        LLL: 'MMMM d, yyyy h:mm T',
        LLLL: 'dddd, MMMM d, yyyy h:mm T'
      },
      /**
       * This is only used with the customDateFormat plugin
       */
      ordinal: (n) => n,
      /**
       * This is only used with the customDateFormat plugin
       */
      format: 'L'
    }
  }
)
  

today

Defaults: Go to today

clear

Defaults: Clear selection

close

Defaults: Close the picker

selectMonth

Defaults: Select Month

previousMonth

Defaults: Previous Month

nextMonth

Defaults: Next Month

selectYear

Defaults: Select Year

previousYear

Defaults: Previous Year

nextYear

Defaults: Next Year

selectDecade

Defaults: Select Decade

previousDecade

Defaults: Previous Decade

nextDecade

Defaults: Next Decade

previousCentury

Defaults: Previous Century

nextCentury

Defaults: Next Century

pickHour

Defaults: Pick Hour

incrementHour

Defaults: Increment Hour

decrementHour

Defaults: Decrement Hour

pickMinute

Defaults: Pick Minute

incrementMinute

Defaults: Increment Minute

decrementMinute

Defaults: Decrement Minute

pickSecond

Defaults: Pick Second

incrementSecond

Defaults: Increment Second

decrementSecond

Defaults: Decrement Second

toggleMeridiem

Defaults: Toggle Period

selectTime

Defaults: Select Time

selectDate

Defaults: Select Date

dayViewHeaderFormat

Accepts: DateTimeFormatOptions Defaults: { month: 'long', year: '2-digit' }
This should be an appropriate value from the Intl.DateFormat options.

locale

Defaults: default
This should be a BCP 47 language tag or a value supported by Intl.

startOfTheWeek

Accepts: 0-6 Defaults: 0
Changes the start of the week to the provided index. Intl/Date does not provide apis to get the locale's start of the week. 0 = Sunday, 6 = Saturday. If you want the calendar view to start on Monday, set this option to 1.

dateFormats

These options describe shorthand format strings.

LTS

Long form time format.

LT

Short time format.

L

Standard date format.

LL

Long form date format. US default is July 4, 2022.

LLL

Long form date/time format. US default is July 4, 2022 9:30 AM.

LLLL

Long form date/time format with weekday. US default is Monday, July 4, 2022 9:30 AM.

ordinal

Function to convert cardinal numbers to ordinal numbers, e.g. 3 -> third.

format

Default tokenized format to use. This can be "L" or "dd/MM/yyyy".

Localization Options 08/11/2022 08/11/2022 How to use the restriction options. datepicker, javascript, open source, tempus dominus, eonasdan