Image copyright Getty Images Image caption Pikachu was originally referred to in Hong Kong as Beikaciu, which sounds phonetically close to its name in Japanese

Japanese game-maker Nintendo is about to release two new games in its hugely popular Pokemon series.

But a decision to use only Mandarin Chinese names for the characters has proved controversial in Hong Kong.

The BBC looks at why fans and linguists are so riled.

1. What's in a name - Beikaciu or Pikaqiu?

Image copyright AFP Image caption The decision by Nintendo is seen in the current climate as "mainlandisation"

Pokemon characters' names used to be translated differently in different parts of the Chinese-speaking world, to reflect local pronunciation. Hence, the hugely beloved Pikachu was known for decades as Bei-Ka-Ciu in Hong Kong, and Pi-Ka-Qiu in mainland China.

But Nintendo announced earlier this year that it would be unifying the names of more than 100 Pokemon characters, and has renamed many of them according to the Mandarin translations.

Both Cantonese and Mandarin speakers read Chinese, although people in Hong Kong use the traditional Chinese script while people on mainland China use simplified Chinese.

However, the same words can be pronounced differently in each language.

For example, Pikachu's new official Chinese name, 皮卡丘, is pronounced Pi-Ka-Qiu in Mandarin. But in Cantonese, the characters would be pronounced Bei-Ka-Jau - which Hong Kong critics argue sound nothing like Pikachu's original name.

2. It's about identity

More than 6,000 people signed a petition in March asking Nintendo to reverse its decision. Then on Monday dozens of people protested at the Japanese consulate.

For a small but vocal group, the move has hit a nerve.

"Our main point is that the translation ignores Hong Kong's culture," said a spokesman from a Facebook group known as Petition to keep Regional Chinese Translations of Pokemon. "There's no respect for it."

Image copyright Reuters Image caption The pro-democracy movement saw tens of thousands of Hong Kong citizens take to the streets

"We are aware of the reasons behind Nintendo's translation, presumably to make it easier for purposes such as publicity, but the move ignores a lot of players. We hope the Hong Kong market can be taken seriously and treated sincerely."

The BBC's Juliana Liu in Hong Kong says the dispute taps into growing local fears that Cantonese - along with local culture and tradition - is being supplanted by Mandarin.

Prof Stephen Matthews of the School of Humanities, University of Hong Kong, agrees.

"It's seen in the current climate as creeping 'mainlandisation'," he said.

"In the last few years people have felt that what makes Hong Kong special is disappearing bit by bit and what is an issue of Pokemon which is fairly trivial, becomes a big one because it's very sensitive."

Just months ago, there were violent clashes between so-called "localist" anti-Beijing groups and police, in a dispute over food stalls.

3. It's about language

Last year, the city's Education Bureau caused an uproar when it suggested that Cantonese was not an official language, our correspondent says.

Hong Kong residents, supported by many linguists, believe Cantonese is a proper language, on par with Mandarin.

Image copyright Getty Images Image caption Cantonese is seen by its people as an ancient language, retaining a greater aesthetic similarity to traditional Chinese characters, Prof Matthews tells the BBC

"I think language is perhaps one of the most important things that marks Hong Kong from the rest of China," said Prof Matthews.

"It's crystal clear that Mandarin speakers cannot understand Cantonese and vice versa. They are not mutually intelligible."

But in mainland China itself, the dizzyingly diverse range of regional forms of speech are known only as dialects, not languages in their own right.

Earlier in February, Hong Kong officials received more than 10,000 complaints in three days after a TV programme began using subtitles in mainland Chinese characters instead of Hong Kong's traditional script.

4. It's about the 'collective memory of a generation'

Hong Kong activist group Civic Passion organised Monday's demonstration.

"Pikachu has been in Hong Kong for more than 20 years," said Sing Leung, one of those who took part.

"It is not simply a game or comic book, it is the collective memory of a generation."

"It was a good decision for them to launch a Chinese version of the game, but it has not respected the culture and language of specific places."