Because no versions of charts_flutter match >0.9.0 <0.10.0 and charts_flutter 0.9.0 depends on intl >=0.15.2 <0.17.0, charts_flutter ^0.9.0 requires intl >=0.15.2 <0.17.0.
And because every version of flutter_localizations from sdk depends on intl 0.17.0-nullsafety.2, charts_flutter ^0.9.0 is incompatible with flutter_localizations from sdk.
Because no versions of charts_flutter match >0.9.0 <0.10.0 and charts_flutter 0.9.0 depends on intl >=0.15.2 <0.17.0, charts_flutter ^0.9.0 requires intl >=0.15.2 <0.17.0.
And because every version of flutter_localizations from sdk depends on intl 0.17.0-nullsafety.2, charts_flutter ^0.9.0 is incompatible with flutter_localizations from sdk.