@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Bean
    public LocaleResolver localeResolver() {
        //设置cookie模式处理国际化
        CookieLocaleResolver cookieLocaleResolver = new CookieLocaleResolver();
        cookieLocaleResolver.setDefaultLocale(Locale.CHINESE);
        return cookieLocaleResolver;
    }
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //指定国际化标识
        LocaleChangeInterceptor localeChangeInterceptor = new LocaleChangeInterceptor();
        localeChangeInterceptor.setParamName("lang");
        registry.addInterceptor(localeChangeInterceptor);
    }
}

// 1.需指定名称替换默认bean
@Component("messageSource")
public class DBMessageSource extends AbstractMessageSource {
    // 自定义service
    @Autowired
    private LanguageRepository languageRepository;
    // 2.国际化处理方法依据key在数据库中查找对应国际化内容
    @Override
    protected MessageFormat resolveCode(String key, Locale locale) {
        LanguageEntity message = languageRepository.findByKeyAndLocale(key,locale.getLanguage());
        if (message == null) {
            message = languageRepository.findByKeyAndLocale(key,Locale.getDefault().getLanguage());
        }
        return new MessageFormat(message.getContent(), locale);
    }
    //3.新增方法，用于后端传参国际化
    public final String getMessage(String code, @Nullable Object[] args) throws NoSuchMessageException {
        Locale locale = LocaleContextHolder.getLocale();
        String msg = getMessageInternal(code, args, locale);
        if (msg != null) {
            return msg;
        }
        String fallback = getDefaultMessage(code);
        if (fallback != null) {
            return fallback;
        }
        throw new NoSuchMessageException(code, locale);
    }
}

<h2 th:text="#{home.welcome('xxx')}"></h2>
<p th:text="#{home.info}"></p>
<p th:text="#{home.changelanguage}"></p>
<ul>
    <li><a href="?lang=en" th:text="#{home.lang.en}"></a></li>
    <li><a href="?lang=de" th:text="#{home.lang.de}"></a></li>
    <li><a href="?lang=zh" th:text="#{home.lang.zh}"></a></li>
</ul>