client: updates for zh-CN

[chappjc]

Updates for zh-CN translations.

This PR is a massaged version of #1863

[chappjc]

client/webserver/locales/zh-cn.go

Warning: no zh-CN replacement text for key "txfee_not_available", using 'en' value Transaction fee currently unavailable

dcrdex/client/webserver/locales/en-us.go

Line 284 in 208268a

"txfee_not_available": "Transaction fee currently unavailable",

client/core/locale_ntfn.go

7 missing notification translations for zh-CN
[zh-CN] Translation missing for topic RedemptionResubmitted
[zh-CN] Translation missing for topic RedemptionConfirmed
[zh-CN] Translation missing for topic WalletCommsWarning
[zh-CN] Translation missing for topic SwapRefunded
[zh-CN] Translation missing for topic WalletPeersWarning
[zh-CN] Translation missing for topic WalletPeersRestored
[zh-CN] Translation missing for topic QueuedCreationFailed

2 stale notification translations for zh-CN
[zh-CN] Translation stale for topic SendError
[zh-CN] Translation stale for topic SendSuccess

dcrdex/client/core/locale_ntfn.go

Line 342 in 208268a

TopicRedemptionResubmitted: {

(and neighboring)

dcrdex/client/core/locale_ntfn.go

Lines 702 to 711 in 208268a

	TopicSendError: {
	subject: "提款错误",
	template: "在 %s 提取过程中遇到错误: %v", // alt. 删除 %s 时遇到错误： %v
	stale: true,
	},
	// [value string, ticker, destination address, coin ID]
	TopicSendSuccess: {
	subject: "提款已发送",
	template: "%s %s (%s) 的提款已成功完成。硬币 ID = %s",
	stale: true,

[chappjc]

These don't translate properly?

[chappjc]

Slightly behind because the frontend is such a moving target, but I don't think we need to hold up this update as long as it doesn't break anything.