Support react-i18next "defaults" prop

Support react-i18next "defaults" prop: a task in MiMo-V2.6-RL-oss: Agentic RL Environments (MiMo RL release). Version i18next: <i 11.2.2</i i18next-scanner: <i 2.4.6</i react-i18next: <i 7.7.0</i Configuration react-i18n v7.7.0 introduced the defaults prop (see i18next/react-i18next 439). I expect…