The modern Mother’s Day is celebrated on various days in many parts of the world,
most commonly in May or in March/April, as a day to honour mothers and motherhood.
In the UK and Ireland it follows the old traditions of Mothering Sunday, celebrated in March/April.

More info at Wikipedia.

1 January
Iran

9 January
Israel (Family Day)

11 February
Norway

3 March
Georgia

8 March (with International Women’s Day)
Albania, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Bulgaria, Burundi, Burkina Faso, Kazakhstan, Kosovo, Laos, Moldova, Montenegro, North Macedonia, Russia, Serbia, Tajikistan, Uzbekistan, Vietnam

10 March (Mothering Sunday)
Guernsey, Ireland, Isle of Man, Jersey, Nigeria, United Kingdom

21 March (Spring equinox)
Bahrain, Comoros, Djibouti, Egypt, Iraq, Jordan, Kuwait, Libya, Lebanon, Mauritania, Oman, Palestine, Qatar, Saudi Arabia, Somalia, Sudan, Syria, United Arab Emirates, Yemen

25 March
Slovenia

7 April (Annunciation day)
Armenia (Motherhood and Beauty Day)

Between 19 April and 19 May
Nepal

5 May (First Sunday of May)
Angola, Cape Verde, Hungary, Lithuania, Mozambique, Romania, Portugal, São Tomé and Príncipe, Spain

8 May
South Korea (Parents’ Day)

10 May
El Salvador, Guatemala, Mexico

12 May (Second Sunday of May)
Anguilla, Antigua and Barbuda, Aruba, Australia, Austria, Bahamas, Bangladesh, Barbados, Belgium, Belize, Bermuda, Bhutan, Bonaire, Botswana, Brazil, Brunei, Canada, Cambodia, Cayman Islands, Central African Republic, Chad, Chile, China, Colombia, Congo, Dem. Rep., Congo, Rep., Cote d’Ivoire, Croatia, Cuba, Curaçao, Cyprus, Czech Republic, Denmark, Dominica, Ecuador, Equatorial Guinea, Estonia, Ethiopia, Faroe Islands, Fiji, Finland, Gabon, Gambia, Germany, Ghana, Greece, Greenland, Grenada, Guyana, Honduras, Hong Kong, Iceland, India, Italy, Jamaica, Japan, Kenya, Latvia, Liberia, Liechtenstein, Macau, Malaysia, Malta, Myanmar, Namibia, Netherlands, New Zealand, Pakistan, Papua New Guinea, Peru, Philippines, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Samoa, Singapore, Sint Maarten, Slovakia, South Africa, Sri Lanka, Suriname, Switzerland, Taiwan, Tanzania, Tonga, Trinidad and Tobago, Turkey, Uganda, Ukraine, United States, Uruguay, Vietnam, Venezuela, Zambia, Zimbabwe

14 May
Benin

15 May
Paraguay (same day as Día de la Patria)

19 May
Kyrgyzstan (Russian: День матери, Kyrgyz: Энэ күнү)

26 May
Poland (Polish: Dzień Matki)

27 May
Bolivia

28 May (Last Sunday of May)
Algeria, Cameroon, Dominican Republic, Haiti, Madagascar, Mali, Mauritius, Morocco, Niger, Senegal, Sweden, Tunisia

4 June
France, French Antilles

30 May
Nicaragua

1 June (together with Children’s Day)
Mongolia

11 June (Second Sunday of June)
Luxembourg

14 June
Afghanistan

3 July(First Monday of July)
South Sudan

1 August
Vietnam (Vu-lan Báo Hiếu)

12 August
Thailand (birthday of Queen Sirikit)

15 August (Assumption of Mary)
Antwerp (Belgium), Costa Rica

14 October
Belarus

16 October
Malawi

20 October
Vietnam (Vietnamese Women’s Day)

15 October
Argentina (Día de la Madre)

3 November
Timor Leste

16 November
North Korea

Last Sunday of November
Russia

8 December (Feast of the Immaculate Conception)
Panama

22 December
Indonesia (Hari Ibu)